Install preloaded-classes as a standalone configuration file

Install preloaded-classes as a standalone configuration file
/system/etc/preloaded-classes, so we can configure different file per product.
To override the default frameworks/base/preloaded-classes, just override
in your product configuration makefile with PRODUCT_COPY_FILES before it
inherits from build/target/product/base.mk: if there are multiple items
in PRODUCT_COPY_FILES with the same destination, the first one takes
precedence.

Bug: 18305157
Change-Id: I937632b4a1aa73310ec90e73fd708fbd0c704a21