Choose latest build-tools version by default

Also allow specifying build tools version manually by adding
:build-tools-version option to :android map
Rework handling of :user profile

Some potentially incompatible options are now removed from :user profile.
Also system-wide :android-debug and :android-release profiles were introduced.
Minor tidying-up
Create ".nrepl-port" file instead of "repl-port"
Add few extra files to a "new" template
Update sample file
Update dependency versions
Prepare 0.2.3 release