ARMORY-142 - Watch-Only Data Export - Bug fixes

Fixed multiple bugs related to the watch-only wallet data export (aka
the public key/chain code export). They include:

-The code not running due to a misnamed variable.
-The export format being changed to text-only.
-PKCC references being changed to "watch-only data" so that people
aren't overwhelmed with data they don't need to know about.

Further changes to the GUI may be forthcoming.