build: Add support for PRODUCT_COPY_FILES_OVERRIDES

 * We may have a case where prebuilts need to be built from
   source instead based on an externalized config.
 * New directive takes a list of destination files to remove from
   PRODUCT_COPY_FILES so that other instructions can be supplied.

Change-Id: I7feff16440e54d1676ffddbbd96d5947efa43ede
Move emulator.mk out of full_base.mk

Instead we should have the emulator products (full, full_mips, full_x86,
sdk) inherit from emulator.mk directly, because full_base.mk is also
inherited by real device products, such as full_manta.mk.

Conflicts:
	target/product/full_base.mk

Change-Id: I6f5f9255c73be8a4cfad7ddf88c4b633b05a7091
Merge remote-tracking branch 'cm/cm-11.0' into cm-11.0