update the UI to accommodate the sync features from gqrx-hamlib

[Marzona]

As discussed with Simon, we are going to merge into rig-remote the features of https://github.com/g0fcu/gqrx-hamlib.

This issue is tracking the work required to update the UI to provide access to the feature provided by gqrx-hamlib. The changes that I foresee as of now are:

• something a checkbutton that once pressed will trigger the code that fetches the frequency from hamlib and sets the same to gqrx every 0.X seconds.
• a small form that would allow for rigtctl endpoint configuration
• a confirmation signal (like a text that becomes green, or flashes or whatever) that is a visual information that the sync is on

There are other UI changes in other sims that are impacting the UI:

• https://github.com/Marzona/rig-remote/issues/8
• https://github.com/Marzona/rig-remote/issues/9
• https://github.com/Marzona/rig-remote/issues/2