new drawable resources
add <merge> and <include> to layout resource
update drawable class descriptioons to point to resources guide
add ID resource type
Change-Id: I733eec50bb2671f28c9e6dd7dec14eb6586f5193
docs: rewrite resources documentation
Huge overhaul. Includes all new dev guides about how resources are used
on Android and how to provide alternatives, including how to handle
runtime configuration changes (restarts). Plus all new reference
docs for all the resource types (drawables, strings, menus, etc.).
Change-Id: I12e819d2c5fc11e062281d8fe442c3037e92000a
