full param interface usability

The full param interface has some usability issues, both in full param tree and full param list
for params with "@Values" we need a drop down of values. In the above you can see user needs to enter a value, and the possible values are unreadable
here is MAVProxy for comparison:

Start by locating the full param tree and full param list interfaces, then inspect how parameters with "@Values" are displayed. Compare the current presentation with the screenshots and verify that possible values are readable and selectable from a drop-down in both interfaces.

Written by the indexing model from the issue text.