Move all database queries off the ui thread & add a ViewModel for MainActivity (#4786)

- Move all database queries off the ui thread - this is a massive
performance improvement
- ViewModel for MainActivity - this makes MainActivity smaller and
network requests won't be retried when rotating the screen
- removes the Push Notification Migration feature. We had it long
enough, all users who want push notifications should be migrated by now
- AccountEntity is now immutable
- converted BaseActivity to Kotlin
- The header image of Accounts is now cached as well

app/src/main/java/com/keylesspalace/tusky/interfaces/AccountActionListener.kt

@@ -18,5 +18,5 @@ interface AccountActionListener {
     fun onViewAccount(id: String)
     fun onMute(mute: Boolean, id: String, position: Int, notifications: Boolean)
     fun onBlock(block: Boolean, id: String, position: Int)
-    fun onRespondToFollowRequest(accept: Boolean, id: String, position: Int)
+    fun onRespondToFollowRequest(accept: Boolean, accountIdRequestingFollow: String, position: Int)
 }

app/src/main/java/com/keylesspalace/tusky/interfaces/FabFragment.kt

@@ -1,22 +0,0 @@
-/*
- * Copyright 2023 Tusky Contributors
- *
- *  This file is a part of Tusky.
- *
- *  This program is free software; you can redistribute it and/or modify it under the terms of the
- *  GNU General Public License as published by the Free Software Foundation; either version 3 of the
- *  License, or (at your option) any later version.
- *
- *  Tusky is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
- *  the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
- *  Public License for more details.
- *
- *  You should have received a copy of the GNU General Public License along with Tusky; if not,
- *  see <http://www.gnu.org/licenses>.
- */
-
-package com.keylesspalace.tusky.interfaces
-
-interface FabFragment {
-    fun isFabVisible(): Boolean
-}