some more translatable strings, updating gajim.pot and greek gajim.po [100%]. I think it should be ok now but you never know

better strings [not more clear but TYPOS in English and unknown words] {so I had to break the string being frozen} {sorry for that}
also introducing greek transl [half tooltips remain with english text, but 0.7 can live with it if I do not get to finish it before 0.7]