Having the export button at the top was confusing people into thinking
the entire wallet was exported.
This commit moves the export button to the address book, receiving
addresses and transaction tabs separately.
- use labelExplanation for sending and receiving tab and move the string
from the ui-file to the source
- ensure that the table holding the label and address is resized so that
the address column fits the address and the label column is stretched to
fit the window size
- rename some stuff for much easier readbility in the code (I find it hard
to get the meaning of stuff like labels or buttons)
- add UI-feedback via QValidatedLineEdit
- copy button for generated signature was moved to the signature output field
- add an addressbook button to verify message tab
- input fields are now evenly ordered for sign and verify tabs
- update FIRST_CLASS_MESSAGING support to ensure a good UX
- add a button and context menu entry in addressbook for verify message (to be consistent with sign message)
- focus is now only set/changed, when clearing input fields or adding an address via addressbook
- re-work / update some strings
- ensure model gets initialized in the SignVerifyMessageDialog constructor
- add checks for a valid model to both addressbook buttons
- remove unneeded includes for Qt GUI elements that are listed in ui_signverifymessagedialog.h anyway
