[GUI] Rename titles for buttons in main window
[GUI] Rename titles for buttons in main window

In English words usually more short than in other langs.
Panel with buttons just don't fit inline on Spanish/German/Russian
 * Send coins -> Send, Receive coins -> Receive
This is e-wallet. What user can send and receive? Only coins
 * Address Book -> Contacts
Simplification without loss of meaning

jlay11/sharecoin,jlay11/sharecoin,jlay11/sharecoin,jlay11/sharecoin,jlay11/sharecoin,jlay11/sharecoin