qt: Handle address purpose in incremental updates

Correctly use the purpose of addresses that are added after the start
of the client. Addresses with purpose "refund" and "change" should not
be visible in the GUI. This is now handled correctly.
qt: Display txfee in first sendCoinsDialog message box

Signed-off-by: Jonas Schnelli <jonas.schnelli@include7.ch>
Merge pull request #2951 from laanwj/2013_08_addressbook_purpose

[Qt] Handle address purpose in incremental updates
Fix typo in a comment: it's base58, not base48.
Merge pull request #2967 from tstranex/master

Fix typo in a comment: it's base58, not base48.
Merge pull request #2958 from laanwj/2013_08_txfee2

[Qt] Display txfee in first sendCoinsDialog message box