Open from homescreen/add shortcut to launcher (#435)

* Add very basic "Add to homescreen" action in manga info fragment.

* Fix open from homescreen opening current manga (if a manga is open).
Code cleanup.

* Improve fix for "Opening from homescreen opens currently open manga if a manga is currently open" and fix "Going back to the main app via a Manga opened through a shortcut repeats the launcher open animation".

* Implement custom icons, add star icon and optimize some things.

* Remove Tachiyomi and custom image icon types.

* Move icon creation task into an observable.
Added some extra error handling.

app/src/main/res/drawable/ic_home_white_24dp.xml

@@ -0,0 +1,9 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+        android:width="24dp"
+        android:height="24dp"
+        android:viewportWidth="24.0"
+        android:viewportHeight="24.0">
+    <path
+        android:fillColor="#ffffff"
+        android:pathData="M10,20v-6h4v6h5v-8h3L12,3 2,12h3v8z"/>
+</vector>