bring back DPI changer

originally part of DPI Changer + Tablet UI commit on ICS by @sethyx and @dagr8
cherry-picked and adapted for JB-MR1 by @championswimmer and @kecinzer

PS4:Added situation that values don't exists in build.prop
PS5:
After hour of play with this condition in IntelliJ IDEA I finaly found solution for it.
I must compare .lengtg() to 0. Now it works.
Still I think, that we need clean up all dialog, because clearing Market stuff is no logner needed.

PS6: we are keeping the long procedure intact because we never know
if some day play store starts checking persis.lcd_density too,
so let's keep the compatibility workarounds,
even though atm they are not needed

Change-Id: I3e3a63eb64b0f107c1fad0f2fd8bb7c7f6e6e227
Signed-off-by: ChampionSwimmer <android@championswimmer.tk>
Signed-off-by: task650 <task650@gmail.com>

Conflicts:
	res/xml/lcd_density_setup.xml
	src/com/aokp/romcontrol/fragments/DensityChanger.java
	src/com/aokp/romcontrol/fragments/UserInterface.java