Improve image placeholders

- Show placeholders until the image is loaded because timeout can be very long and missing profile pictures and video thumbnails make app inconvenient to use

- Adapt profile picture and video thumbnail placeholders to light theme

- Replace profile picture and video thumbnail placeholders with vector graphics

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

@@ -18,7 +18,7 @@
         android:layout_centerHorizontal="true"
         android:layout_margin="2dp"
         android:contentDescription="@string/detail_uploader_thumbnail_view_description"
-        android:src="@drawable/buddy_channel_item"
+        android:src="@drawable/buddy"
         app:shapeAppearance="@style/CircularImageView"
         tools:ignore="RtlHardcoded" />
 

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

@@ -17,7 +17,7 @@
         android:layout_centerVertical="true"
         android:layout_marginStart="3dp"
         android:layout_marginRight="15dp"
-        android:src="@drawable/buddy_channel_item"
+        android:src="@drawable/buddy"
         app:shapeAppearance="@style/CircularImageView"
         tools:ignore="RtlHardcoded" />
 

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

@@ -17,7 +17,7 @@
         android:layout_centerVertical="true"
         android:layout_marginStart="3dp"
         android:layout_marginRight="15dp"
-        android:src="@drawable/buddy_channel_item"
+        android:src="@drawable/buddy"
         app:shapeAppearance="@style/CircularImageView"
         tools:ignore="RtlHardcoded" />
 

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

@@ -22,7 +22,7 @@
             android:layout_width="48dp"
             android:layout_height="48dp"
             app:shapeAppearance="@style/CircularImageView"
-            tools:src="@drawable/buddy_channel_item" />
+            tools:src="@drawable/buddy" />
 
         <org.schabi.newpipe.views.NewPipeTextView
             android:id="@+id/title_view"