initial apklib dependency implementation

change library-projects setting to task
naively ignore missing classes.jar files (for apklibs)
Further refine apklib support

put more features into LibraryProject, remove
naive existence check on classes.jar
handle assets from multiple projects by collecting into bin/assets
0.4.0: apklib support, better sdk error, better asset handling
change overwrite=false in asset copyDirectory
Merge branch 'master' into sbt-0.11

Conflicts:
	project/build.properties
ignore missing 'res' directories
Merge branch 'master' into sbt-0.11