Timeline paging (#2238)

* first setup

* network timeline paging / improvements

* rename classes / move to correct package

* remove unused class TimelineAdapter

* some code cleanup

* remove TimelineRepository, put mapper functions in TimelineTypeMappers.kt

* add db migration

* cleanup unused code

* bugfix

* make default timeline settings work again

* fix pinning statuses from timeline

* fix network timeline

* respect account settings in NetworkTimelineRemoteMediator

* respect account settings in NetworkTimelineRemoteMediator

* update license headers

* show error view when an error occurs

* cleanup some todos

* fix db migration

* fix changing mediaPreviewEnabled setting

* fix "load more" button appearing on top of timeline

* fix filtering and other bugs

* cleanup cache after 14 days

* fix TimelineDAOTest

* fix code formatting

* add NetworkTimeline unit tests

* add CachedTimeline unit tests

* fix code formatting

* move TimelineDaoTest to unit tests

* implement removeAllByInstance for CachedTimelineViewModel

* fix code formatting

* fix bug in TimelineDao.deleteAllFromInstance

* improve loading more statuses in NetworkTimelineViewModel

* improve loading more statuses in NetworkTimelineViewModel

* fix bug where empty state was shown too soon

* reload top of cached timeline on app start

* improve CachedTimelineRemoteMediator and Tests

* improve cached timeline tests

* fix some more todos

* implement TimelineFragment.removeItem

* fix ListStatusAccessibilityDelegate

* fix crash in NetworkTimelineViewModel.loadMore

* fix default state of collapsible statuses

* fix default state of collapsible statuses -tests

* fix showing/hiding media in the timeline

* get rid of some not-null assertion operators in TimelineTypeMappers

* fix tests

* error handling in CachedTimelineViewModel.loadMore

* keep local status state when refreshing cached statuses

* keep local status state when refreshing network timeline statuses

* show placeholder loading state in cached timeline

* better comments, some code cleanup

* add TimelineViewModelTest, improve code, fix bug

* fix ktlint

* fix voting in boosted polls

* code improvement

app/build.gradle

@@ -175,4 +175,6 @@ dependencies {
     androidTestImplementation "androidx.room:room-testing:$roomVersion"
     androidTestImplementation "androidx.test.ext:junit:1.1.2"
     testImplementation "androidx.arch.core:core-testing:2.1.0"
+
+    testImplementation 'org.jetbrains.kotlinx:kotlinx-coroutines-test:1.5.0'
 }