Add OpenWrt and OpenWrt package repos as submodules.
Do not ignore submodule directories.
Update submodules as such instead of as independent repos.

This makes update targets pointless since the current version is bound to
particular versions of submodules, not to the latest ones.
Get CONFINE_VERSION straight from the current branch name.

To use a different version the user should simply checkout that branch
instead.
Remove mentions to CONFINE_VERSION from README.
Get git branch and revision inside of confine-system makefile.

The package is part of the main repository anyway.  Also it does not suggest
that OpenWrt's makefile understands these variables.
Remove redundant messages already printed by target "prepare".
Empty submodule directories using git commands.
Remove trailing whitespace and other aesthetic whitespace changes.