Most important:
Change Download dialog to select path there.
Every user query triggers new download of version file, possibly stops former download (with dialog).
Some functions refactored.
A static symbol Slic3r::SEMVER is introduced, which holds
the running slicer's Semver object.
This is mainly done to make testing updater behaviour
_much_ easier. Additionaly to cleanup some questionable code
(Semver was being parsed multiple times / in multiple places
in the frontend.)
