Pointier point releases

[Daniel van Vugt]

I notice how non-trivial it is to update all the projects, rebuilds and 
packages every time we need to integrate a new Mir release into touch.

But we could make this much easier if the Mir team consciously separated 
ABI-break releases from smaller (and more frequent) minor releases. This 
would allow us to install most smaller Mir releases without having to 
update any other projects/packages. It just requires a little planning 
by the Mir team to somehow "save up" and separate ABI-changing 
proposals. I think the trouble might be worthwhile for the benefit we'd 
get in being able to do instant system integration testing on touch images.

For example, given we roughly do a Mir release every 2-3 weeks now, we 
could instead do:

A minor release more often, every week or so (no ABI changes).
A larger release (ABI break) with more intrusive changes less often 
(like monthly?).

- Daniel