FontAwesome 5

Closes #982 (closed)

Replaces all icons with FA5 counterparts. Removes Fontello

Some icons changed to a (slightly) different icon:

• All spinners were changed to circle-notch since FA doesn't have any spinners beyond 7-dots and circle-notch ones.
• bell-ringing is instead a frankenstein of bell and two rss icons to simulate ringing, since bell-on is a FA PRO icon :/
• Video icon (in hidden attachment placeholder) uses generic camera
• Poll icon uses horizontal poll icon, i.e. similar to graph but horizontal and inside a square.
• Smile icon uses beam version, i.e. it does the ^_^ expression. Because people complained that plain :) "stares at them"
• Smile icon in post form changed to filled variant for better harmony with other icons
• globe is changed to a generic "basketball"
• lock now has shackle turned over for better accessibility
• ellipsis in usercard is vertical instead of horizontal
• version tab in settings is now information without circle.
• notifications tab in settings is non-ringing bell
• maybe more i can't remember.

Some small bugfixes:

• Icons in navbar have been readjusted
• Icons in user-card have been readjusted and given MUCH bigger hitbox + better hover indication.
• Some components like RetweetButton have been refactored.
• Some components's CSS was changed to fit better with our guidelines.

src/components/emoji_picker/emoji_picker.js

 import Checkbox from '../checkbox/checkbox.vue'
+import { library } from '@fortawesome/fontawesome-svg-core'
+import {
+  faBoxOpen,
+  faStickyNote,
+  faSmileBeam
+} from '@fortawesome/free-solid-svg-icons'
+
+library.add(
+  faBoxOpen,
+  faStickyNote,
+  faSmileBeam
+)
 
 // At widest, approximately 20 emoji are visible in a row,
 // loading 3 rows, could be overkill for narrow picker
@@ -177,13 +189,13 @@ const EmojiPicker = {
         {
           id: 'custom',
           text: this.$t('emoji.custom'),
-          icon: 'icon-smile',
+          icon: 'smile-beam',
           emojis: customEmojis
         },
         {
           id: 'standard',
           text: this.$t('emoji.unicode'),
-          icon: 'icon-picture',
+          icon: 'box-open',
           emojis: filterByKeyword(standardEmojis, this.keyword)
         }
       ]