Drop support for kitkat; Bump minSdk to 21

This has been dead for a while already, remove the code and bump minSdk to a
version that actually works

Signed-off-by: Aayush Gupta <aayushgupta219@gmail.com>

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

@@ -20,6 +20,6 @@
 <shape xmlns:android="http://schemas.android.com/apk/res/android"
     android:shape="rectangle">
     <corners android:radius="8dp" />
-    <solid android:color="@color/colorShimmer" />
+    <solid android:color="?colorShimmer" />
 </shape>