Fix off-by-one errors in use of IsFinalTx()

Previously CreateNewBlock() didn't take into account the fact that
IsFinalTx() without any arguments tests if the transaction is considered
final in the *current* block, when both those functions really needed to
know if the transaction would be final in the *next* block.

Additionally the UI had a similar misunderstanding.

Also adds some basic tests to check that CreateNewBlock() is in fact
mining nLockTime-using transactions correctly.

Thanks to Wladimir J. van der Laan for rebase.
[Qt] harmonize strings used when exporting in addressbookpage
Merge pull request #3579

f3005c8 [Qt] harmonize strings used when exporting in addressbookpage (Philip Kaufmann)
qt: Translation update

Update English .ts file from source as well as pull changes from transifex
to current translation.
Merge pull request #2342

665bdd3 Fix off-by-one errors in use of IsFinalTx() (Peter Todd)
[Qt] Fix coin control labels update