Armory offline

Submitting  this PR to get some feedback on the flow and UI, so far it has been tested for send only.

I think the broadcast functionality would be better placed in the "My Addresses" section on the address options, since the broadcast is for any MP transaction, not only for send.

TODO:
- Support for issuing assets/crowdsales
- Support for DEx operations

The address is available to select for any of those actions, so maybe it shouldn't until the functionality is available for all actions.