[imagebuilder]

[imagebuilder]
	- add a helper script to generate opkg.conf, attempt to detect package architecture from packages/
	- fix package defaults when no package override is given, IB previously aggregated the defautls of all profiles
	- introduce a repositories.conf, allows using remote opkg repositories in imagebuilder

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@22978 3c298f89-4303-0410-b956-a3cf2f4a3e73