Do not increase counter in case of no change
Update user stats on same time as generating Change object (thus accounting every change in suprojects, not counting all just once)
Skip stats updating if there was no change in backend
Set fuzzy after setting content

Otherwise the Po backend is too smart and drops fuzzy flag when the
string is not translated. So creating new fuzzy translation leads to
situation when in database we have the fuzzy flag but not in the
backend.

This inconsistency in database is causing wrong behaviour when togging
fuzzy flag as seen in issue #189.