[Qt] coin-control features GUI cleanup 2

- remove monospace labels from sendcoinsdialog also
- use a validated line edit for the change address
- add a tooltip to change address switch
- ensure we have a valid change address in
  CoinControlDialog::coinControl->destChange or just CNoDestination()
- some small ui file changes
[Qt] coin-control features GUI cleanup 3

- remove style sheets from ui files and use Qt attributes instead
- make some more strings untranslatable, to make life for translators
  easier
- split up long tooltips an rework the texts a little
Merge pull request #3285

d3207b6 [Qt] coin-control features GUI cleanup 3 (Philip Kaufmann)
834e14e [Qt] coin-control features GUI cleanup 2 (Philip Kaufmann)
qt: use deleteLater to remove send entries

Use deleteLater() instead of delete, as it is not allowed
to delete widgets directly in an event handler.
Should solve the MacOSX random crashes on send with coincontrol.
Merge pull request #3355

6c98cca qt: use deleteLater to remove send entries (Wladimir J. van der Laan)
Prevent empty transactions from being added to vtxPrev

CWalletTx::AddSupportingTransactions() was adding empty transaction
to vtxPrev in some cases. Skip over these.

Part one of the solution to #3190. This prevents invalid vtxPrev from
entering the wallet, but not current ones being transmitted.
Refuse to retransmit transactions without vins

Versions of bitcoin before 0.8.6 have a bug that inserted
empty transactions into the vtxPrev in the wallet, which will cause the node to be
banned when retransmitted, hence add a check for !tx.vin.empty()
before RelayTransaction.
Merge pull request #3357

4ef92a9 Refuse to retransmit transactions without vins (Wladimir J. van der Laan)
Merge pull request #3356

d3ef9b0 Prevent empty transactions from being added to vtxPrev (Wladimir J. van der Laan)