cmsdk: include our own consumer proguard rules

Include a proguard file with can be consumed by the latest gradle plugin to
merge this ones rules without the rules of the app linked to.
This way devs doesn't need to declare (in a recent version of the gradle plugin)
-dontwarn and -dontnote for cyanogenmod.library when linked to it, because
proguard crashes the build because it cannot access to cm system private classes.

TICKET: RM-232
Change-Id: I7c94a9119db744b0029b4d9a8aa782adcbd47b93
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>
(cherry picked from commit c6550fd8)