Reduce maximum length when cutting title

MediaWiki has a maximum title file length, which means
that the title may have to be cut according to some rules.

I thought this limit was 256 bytes but it turns out to be
actually 240 bytes (as hinted by the GWToolset).

- Change max length to 240
- Add assertion to ensure it

Note how the limits are in bytes and not characters,
but Python len() method on Unicode strings actually
behaves as expected.
Return string instead of printing directly categorisation statistics

We do not always want this to be printed around.
Prevent empty separators when building titles

The title is generated by formatted strings like
'Blah - <A> - <B> - <C> - Blah.jpg'

But is somehow <B> is empty in the metadata
this results in ugly 'Blah - AA - - CC - Blah.jpg'
We do not want that.
Remove rule for parentheses in title cleaning

It is perfectly legit to have a parenthesis with a space
before. We do not want to remove the space.
Merge branch 'master' of github.com:JeanFred/MassUploadLibrary