Fix dependency handling

Run slapt-src with the -n (--no-deps) option always. Since dependencies
have been calculated and have been put in the queue earlier, that means
that they have been processed already. No need to ask slapt-src to
calculate dependencies again.

Ignore %README% dependencies. slapt-src would fail, trying to find a
SlackBuild named "%README%". SBo folks put that in the REQUIRES field of
the .info file, when they want the user to actually read the README file
before running the SlackBuild. Of course there is no SlackBuild named
"%README%" and so slapt-src (and thus sourcery) would fail in this case.
We're just ignoring it. Users are advised to read the README file in all
cases anyway (and it's easy to do that from within sourcery).
Update translations from transifex

Add new Gaelic (Scottish) and Brasilian Portuguese translation files.
Update all other translations from transifex.
Add a message for missing dependencies

Sourcery was completely ignoring missing dependencies until now. With
this, if any dependency is found to be missing, a dialog pops up and
asks the user to find the missing dependency with GSlapt.
Update translations from transifex
Update sourcery.pot file with new strings