Add some UI for user-defined domain blocks (#6628)

* Keep list of blocked domains

Might be overkill, but I'm trying to follow the same logic as for blocked users

* Add basic domain block UI

* Add the domain blocks UI to Getting Started

* Fix undefined URL in `fetchDomainBlocks`

* Update all known users' domain_blocking relationship instead of just one's

app/javascript/mastodon/features/ui/index.js

@@ -37,6 +37,7 @@ import {
   FavouritedStatuses,
   ListTimeline,
   Blocks,
+  DomainBlocks,
   Mutes,
   PinnedStatuses,
   Lists,
@@ -158,6 +159,7 @@ class SwitchingColumnsArea extends React.PureComponent {
 
           <WrappedRoute path='/follow_requests' component={FollowRequests} content={children} />
           <WrappedRoute path='/blocks' component={Blocks} content={children} />
+          <WrappedRoute path='/domain_blocks' component={DomainBlocks} content={children} />
           <WrappedRoute path='/mutes' component={Mutes} content={children} />
           <WrappedRoute path='/lists' component={Lists} content={children} />