Revert Font Awesome 5 upgrade (#8810)

* Revert "Fix some icon names changed by the Font Awesome 5. (#8796)"

This reverts commit 3f9ec3de82.

* Revert "Migrate to font-awesome 5.0. (#8799)"

This reverts commit 8bae14591b.

* Revert "Fix some icons names, unavailable in fontawesome5 (free license). (#8792)"

This reverts commit b9c727a945.

* Revert "Update the icon name changed by the Font Awesome 5. (#8776)"

This reverts commit 17af4d27da.

* Revert "Add bot icon to bot avatars and migrate to newer version of Font Awesome (#8484)"

This reverts commit 4b794e134d.

app/views/about/_links.html.haml

@@ -13,4 +13,4 @@
     %li
       = link_to 'https://joinmastodon.org/' do
         = "#{t('about.other_instances')}"
-        %i.fa.fa-external-link-alt{ style: 'padding-left: 5px;' }
+        %i.fa.fa-external-link{ style: 'padding-left: 5px;' }

app/views/layouts/modal.html.haml

@@ -9,7 +9,7 @@
         = t 'users.signed_in_as'
         %span.username @#{current_account.local_username_and_domain}
       = link_to destroy_user_session_path(continue: true), method: :delete, class: 'logout-link icon-button' do
-        = fa_icon 'sign-out-alt'
+        = fa_icon 'sign-out'
 
   .container-alt= yield
   .modal-layout__mastodon

app/views/stream_entries/_status.html.haml

@@ -35,7 +35,7 @@
   - elsif pinned
     .status__prepend
       .status__prepend-icon-wrapper
-        %i.status__prepend-icon.fa.fa-fw.fa-thumbtack
+        %i.status__prepend-icon.fa.fa-fw.fa-thumb-tack
       %span
         = t('stream_entries.pinned')