Slim Recents iconpack support [1/3]

ezio:
adapted IconPackHelper from CM trebuchet (https://review.lineageos.org/#/c/136600/

)
with latest OmniSwitch improvements;
splitted the whole dialog part and moved it into Settings;
i've set here Danesh as commit author because he made the original IconPackHelper
code long time ago.

Conflicts:
        core/java/android/provider/Settings.java
Change-Id: If1c8c040506e156a4e4ee9fbd72aa28c13a5f09e
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>