Code cleanup and minimization

* Deduplicated and simplified a lot of code
* Fixed ``invalidSeekConditions`` so that it's possible to seek while the player is loading (like currently the case)

app/src/main/res/layout-large-land/player.xml

@@ -647,24 +647,6 @@
         android:layout_width="match_parent"
         android:layout_height="match_parent">
 
-        <LinearLayout
-            android:layout_width="match_parent"
-            android:layout_height="match_parent"
-            android:gravity="center"
-            android:orientation="vertical">
-
-            <ImageView
-                android:id="@+id/controlAnimationView"
-                android:layout_width="100dp"
-                android:layout_height="100dp"
-                android:background="@drawable/background_oval_black_transparent"
-                android:padding="15dp"
-                android:visibility="gone"
-                tools:ignore="ContentDescription"
-                tools:src="@drawable/ic_fast_rewind"
-                tools:visibility="visible" />
-        </LinearLayout>
-
         <RelativeLayout
             android:id="@+id/loading_panel"
             android:layout_width="match_parent"
@@ -764,8 +746,8 @@
         android:textColor="@color/white"
         android:visibility="gone" />
 
-    <org.schabi.newpipe.views.player.PlayerSeekOverlay
-        android:id="@+id/seekOverlay"
+    <org.schabi.newpipe.views.player.PlayerFastSeekOverlay
+        android:id="@+id/fast_seek_overlay"
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:alpha="0"

app/src/main/res/layout/player.xml

@@ -643,24 +643,6 @@
         android:layout_width="match_parent"
         android:layout_height="match_parent">
 
-        <LinearLayout
-            android:layout_width="match_parent"
-            android:layout_height="match_parent"
-            android:gravity="center"
-            android:orientation="vertical">
-
-            <ImageView
-                android:id="@+id/controlAnimationView"
-                android:layout_width="100dp"
-                android:layout_height="100dp"
-                android:background="@drawable/background_oval_black_transparent"
-                android:padding="15dp"
-                android:visibility="gone"
-                tools:ignore="ContentDescription"
-                tools:src="@drawable/ic_fast_rewind"
-                tools:visibility="visible" />
-        </LinearLayout>
-
         <RelativeLayout
             android:id="@+id/loading_panel"
             android:layout_width="match_parent"
@@ -761,8 +743,8 @@
         android:textColor="@color/white"
         android:visibility="gone" />
 
-    <org.schabi.newpipe.views.player.PlayerSeekOverlay
-        android:id="@+id/seekOverlay"
+    <org.schabi.newpipe.views.player.PlayerFastSeekOverlay
+        android:id="@+id/fast_seek_overlay"
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:alpha="0"

app/src/main/res/layout/player_fast_seek_overlay.xml

@@ -10,8 +10,7 @@
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:clickable="false"
-        android:focusable="false"
-        android:visibility="invisible" />
+        android:focusable="false" />
 
     <org.schabi.newpipe.views.player.SecondsView
         android:id="@+id/seconds_view"