Manifest: adapt for SD from AOSP

CHANGES:
 - Remove all unnecessary device repos (roomservice will handle them)
 - Remove all unnecessary Darwin (Mac OS) repos (we only use Linux, at the moment)
 - Clean up remotes
 - Update README

TO DO:
 - Replace all necessary AOSP repos with SD
 - Replace all necessary GCC with SM (partially done)
 - Add in build script (needs to be updated in SD Vendor, first)

PS3:
 - Remove unused remotes
 - Remove repositories that do not exist
 - Whitespace cleanup

Change-Id: Ieff925ec6fd600f3e08c3d288b91d8015d71dc03
Signed-off-by: Paul Beeler <pbeeler80@gmail.com>
sync manifest to working directory

Change-Id: Ie95cdcf07b8c282bcb0af4bdf762b2edf6fc275b
Signed-off-by: Paul Beeler <pbeeler80@gmail.com>