tx dialog hooks
First cleanup branch commit

This fixes some import and whitespace issues to align closer to pep8.
I added a few comments to make further contributions easier.
Removed uselss comment.
Merge pull request #730 from chrisglass/pep8ing-phase-one

First cleanup branch
fix import
various bugfixes for imported addresses
catch exceptions raised by fiat amount conversion to decimal
minor fix
define frozen signal for exchange rate plugin
remove unused variable.
catch exception within sign thread, to re-enable send button
add missing module qrtextedit
wallet.is_beyond_limit (False for imported accounts)
fix payto size