Piefed feeds.

[olorin99]

Adds feed details for piefed feeds similar to the community details ui. Showing feed title, icon etc.
Adds feed menu with options for showing included communities, editing and saving locally.
Allows editing server feeds.

[jwr1]

Once you save a feed locally, are you free to edit it how you like, or is it just a "bookmark" of the saved feed? I ask because after I saved a feed manually, there was a button next to the newly saved feed on the feeds screen to edit it. And it allowed me to edit it freely, except the save button never became enabled. If this is supposed to be able to edit the feeds and, when saved, update it on the PieFed server as well, then we should probably hide the edit button in general if you aren't the owner in order to prevent confusion.

[jwr1]

When deleting a feed, it just stays on the same screen as if nothing had happened. We probably want to navigate back from there instead.

[jwr1]

If you try to create a new feed with a "Server topic", we just get a null error. I'm not sure if that was introduced in this PR or if PieFed made a change that did this?

[ERROR:flutter/runtime/dart_vm_initializer.cc(40)] Unhandled Exception: Null check operator used on a null value
#0      new FeedModel.fromPiefed (package:interstellar/src/models/feed.dart:96:29)
#1      new FeedModel.fromPiefed.<anonymous closure> (package:interstellar/src/models/feed.dart:94:43)
#2      MappedListIterable.elementAt (dart:_internal/iterable.dart:442:31)
#3      ListIterator.moveNext (dart:_internal/iterable.dart:371:26)
#4      new _GrowableList._ofEfficientLengthIterable (dart:core-patch/growable_array.dart:194:27)
#5      new _GrowableList.of (dart:core-patch/growable_array.dart:154:28)
#6      new List.of (dart:core-patch/array_patch.dart:39:18)
#7      ListIterable.toList (dart:_internal/iterable.dart:224:7)
#8      new FeedModel.fromPiefed (package:interstellar/src/models/feed.dart:95:18)
#9      new FeedListModel.fromPiefed.<anonymous closure> (package:interstellar/src/models/feed.dart:18:38)
#10     MappedListIterable.elementAt (dart:_internal/iterable.dart:442:31)
#11     ListIterator.moveNext (dart:_internal/iterable.dart:371:26)
#12     new _GrowableList._ofEfficientLengthIterable (dart:core-patch/growable_array.dart:194:27)
#13     new _GrowableList.of (dart:core-patch/growable_array.dart:154:28)
#14     new List.of (dart:core-patch/array_patch.dart:39:18)
#15     ListIterable.toList (dart:_internal/iterable.dart:224:7)
#16     new FeedListModel.fromPiefed (package:interstellar/src/models/feed.dart:19:14)
#17     APIFeed.list (package:interstellar/src/api/feed.dart:33:30)
<asynchronous suspension>
#18     _ExploreScreenState._pagingController.<anonymous closure> (package:interstellar/src/screens/explore/explore_screen.dart:113:27)
<asynchronous suspension>
#19     AdvancedPagingController.fetchNextPage (package:interstellar/src/widgets/paging.dart:83:22)
<asynchronous suspension>

[olorin99]

Now if the current account is not the feed owner then the edit button should be disabled and it should act like a bookmark. Also changed the delete button on the edit page to delete the feed on the server.

[olorin99]

Adding new server feeds now creates the feed on the server rather than just searching and saving existing feeds. Existing feeds can still be saved via the explore screen.

[jwr1]

Thanks!