Cleanup rootfs

[ashthespy]

Changes

-- Removing a lot of redundant multistrap config bits (like libraries, dummy packages) since we don't set omitrequired=true, we can remove the libraries that are linked to installed packages.

If the OmitRequired option is set to true, these packages will not be added - whilst useful, this option can easily lead to a useless rootfs. Only the packages specified manually in the configuration files will be used in the calculations - dependencies of those packages will be added but no others.

This then leaves extra libs that are really needed. e.g libavahi-compat-libdnssd-dev for the mdns node package utilised by the back end. Ideally would like to move these all to a new section, to make tracking dependencies simpler. Currently we don't really know/recall what is required for what..

-- Removed some packages --- avahi-discover as we don't need the graphical browser. --- udevil as USB auto-mount is done using node-udev ---pyhton-requests not really sure what it was being used for?

There are quite a few more, like sqlite3 that seems to be removed in the back-end but still remain here, but I guess it's better to discuss/track these in #429

--Streamline and log sizes of the rootfs so we see how it grows/shrinks.

N.B: All our custom dpkg.cfg.d/ rules are not in place when we run multistrap, and I tried playing around getting multistrap to honour them, but didn't succeed. So all the --path-exclude stuff is only valid for installs that are done in chroot later on.. It would be great to not extract everything first, and then delete it in finalize.sh. Minor optimisation, but should think about it..

[volumio]

@ashthespy please wait next time ;) I was still testing it...

[ashthespy]

Oops sorry -- everyone seems to be committing directly to the branch, so wanted to get it in as well before stuff diverges..

[volumio]

@ashthespy all looks good! well done!