Show issue reactions (#421)

```
$ tea issue 230

   #230 issue/pull details: show reactions (open)

  @6543 created 2020-10-22 16:39

  since reactions are utf8 now and most terminals too, we can display them nicely :)

  https://gitea.com/api/v1/repos/gitea/tea/issues/230/reactions

  --------

  1x 🎉  |  1x 👀  |  1x   |  1x 👍  |  1x 👎  |  1x 😆  |  1x 😕  |  1x ❤️
```

caveats:
- reactions are not returned as UTF8 (as was claimed in #230), so they need to be parsed. the library I use doesn't (and can't → ) support all reactions available in gitea
- currently only for issues, as reactions for comments mean an additional API request for each comment..

fixes #230

Co-authored-by: Norwin <git@nroo.de>
Reviewed-on: https://gitea.com/gitea/tea/pulls/421
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: Norwin <noerw@noreply.gitea.io>
Co-committed-by: Norwin <noerw@noreply.gitea.io>

vendor/github.com/enescakir/emoji/README.md

@@ -0,0 +1,99 @@
+# emoji :rocket: :school_satchel: :tada:
+[![Build Status](https://github.com/enescakir/emoji/workflows/build/badge.svg?branch=master)](https://github.com/enescakir/emoji/actions)
+[![godoc](https://godoc.org/github.com/enescakir/emoji?status.svg)](https://godoc.org/github.com/enescakir/emoji)
+[![Go Report Card](https://goreportcard.com/badge/github.com/enescakir/emoji)](https://goreportcard.com/report/github.com/enescakir/emoji)
+[![Codecov](https://img.shields.io/codecov/c/github/enescakir/emoji)](https://codecov.io/gh/enescakir/emoji)
+[![MIT License](https://img.shields.io/github/license/enescakir/emoji)](https://github.com/enescakir/emoji/blob/master/LICENSE)
+
+`emoji` is a minimalistic emoji library for Go. It lets you use emoji characters in strings.
+
+Inspired by [spatie/emoji](https://github.com/spatie/emoji)
+
+## Install :floppy_disk:
+``` bash
+go get github.com/enescakir/emoji
+```
+
+## Usage :surfer:
+```go
+package main
+
+import (
+    "fmt"
+
+    "github.com/enescakir/emoji"
+)
+
+func main() {
+	fmt.Printf("Hello %v\n", emoji.WavingHand)
+	fmt.Printf("I am %v from %v\n",
+		emoji.ManTechnologist,
+		emoji.FlagForTurkey,
+	)
+	fmt.Printf("Different skin tones.\n  default: %v light: %v dark: %v\n",
+		emoji.ThumbsUp,
+		emoji.OkHand.Tone(emoji.Light),
+		emoji.CallMeHand.Tone(emoji.Dark),
+	)
+	fmt.Printf("Emojis with multiple skin tones.\n  both medium: %v light and dark: %v\n",
+		emoji.PeopleHoldingHands.Tone(emoji.Medium),
+		emoji.PeopleHoldingHands.Tone(emoji.Light, emoji.Dark),
+	)
+	fmt.Println(emoji.Parse("Emoji aliases are :sunglasses:"))
+	emoji.Println("Use fmt wrappers :+1: with emoji support :tada:")
+}
+
+/* OUTPUT
+
+    Hello 👋
+    I am 👨‍💻 from 🇹🇷
+    Different skin tones.
+      default: 👍 light: 👌🏻 dark: 🤙🏿
+    Emojis with multiple skin tones.
+      both medium: 🧑🏽‍🤝‍🧑🏽 light and dark: 🧑🏻‍🤝‍🧑🏿
+    Emoji aliases are 😎
+    Use fmt wrappers 👍 with emoji support 🎉
+*/
+```
+
+This package contains emojis constants based on [Full Emoji List v13.0](https://unicode.org/Public/emoji/13.0/emoji-test.txt).
+```go
+emoji.CallMeHand // 🤙
+emoji.CallMeHand.Tone(emoji.Dark) // 🤙🏿
+```
+Also, it has additional emoji aliases from [github/gemoji](https://github.com/github/gemoji).
+```go
+emoji.Parse(":+1:") // 👍
+emoji.Parse(":100:") // 💯
+```
+
+You can generate country flag emoji with [ISO 3166 Alpha2](https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2) codes:
+```go
+emoji.CountryFlag("tr") // 🇹🇷
+emoji.CountryFlag("US") // 🇺🇸
+emoji.Parse("country flag alias :flag-gb:") // country flag alias 🇬🇧
+```
+
+All constants are generated by `internal/generator`.
+
+## Testing :hammer:
+``` bash
+go test
+```
+
+## Todo :pushpin:
+* Add examples to `godoc`
+
+## Contributing :man_technologist:
+I am accepting PRs that add aliases to the package.
+You have to add it to `customEmojis` list at `internal/generator/main`.
+
+If you think an emoji constant is not correct, open an issue.
+Please use [this list](http://unicode.org/emoji/charts/full-emoji-list.html)
+to look up the correct unicode value and the name of the character.
+
+## Credits :star:
+- [Enes Çakır](https://github.com/enescakir)
+
+## License :scroll:
+The MIT License (MIT). Please see [License File](LICENSE.md) for more information.