Simplify titles of tabs in main window

Words in English language are more short than in other langs usually.
Tabs don't fits in line in Spanish/German/Russian when they has two words.
Wallet has limited functionality. It can send & receive coins. So we can
safely rename "Send coins" to "Send" and "Receive coins" to "Receive".
Address book is just user contacts.

This change is affects a translations.
Ported from Freicoin