Settings: Add summary for launch music app when headset is connected

This commit adds a summary for the 'launch music app when headset is
connected' feature. I made this change because in some languages
(e.g. German) the title to descripe this feature got to long for
one line. That just looked aweful.

Before: http://goo.gl/TNDX7
After:  http://goo.gl/PYVme

Change-Id: I67d74e4df5824a8bfaf13dbe708cdef87fbe738c

Conflicts:
	res/values/strings.xml
Settings: Lockscreen Targets Icon Revamp

Adjust the size of custom app icons and resize and round the corners
of gallery icons for a more uniform look.

Before http://imgur.com/cTOqdwX

After http://imgur.com/EKAeFiw

Change-Id: I75f3656ae5b4ac4a4bd1c1cbed6c07ab2863f4fd