FileActivity: don't try to get file from FileDetailSharingFragment
build.gradle: Restore juniversalchardet to 2.0.3
FileDownloader: EXTRA_USER should be User, not Account
SyncedFoldersActivity: cancel loading when activity stops
SyncedFolderAdapter: load thumbnails in parallel instead of sequentially
SyncedFoldersActivity: load content asynchronously
SyncedFoldersActivity: convert to Kotlin (step 2)
SyncedFoldersActivity: conver to Kotlin (step 1)
Update Nextcloud Android library
Update 3rd-party dependencies
