remember last value for Dashware Messages input field

#### Issue details
instead of using a hardwired default for the set of messages to be processed,
remember what the user requested last, or maintain a QComboBox style list of previous values

#### Version
current master

#### Platform
[x] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ ] Rover
[ ] Sub

Locate the Dashware Messages input field and inspect how its current hardwired default is set. Implement remembering the last requested value or retaining previous values in a QComboBox-style list, then verify that the next use restores or offers the prior selection.

Written by the indexing model from the issue text.