Polar-alignment V3. Use plate solving during refresh phase. Update UI.

This is a significant update to polar-alignment. The primary changes are:

• In the refresh phase (when the user is adjusting Az/Alt knobs to correct polar align) plate solving can be used to guide the user, in place of the current "move a chosen star" scheme. The move-star scheme, though, can also be chosen. The advantage to this is that one can fully correct even if the error is larger than the image field-of-view (with move-star, one needed to iterate in that situation). Also, some may prefer this more numerical approach, and (when plate solving is reliable) the intermediate "adjusted" polar-error reporting will be more reliable.
• The UI is simplified (from a code perspective) and updated from a user-facing perspective. There is now an LED panel indicating progress, the on-screen help is updated, there are arrow hints on how to adjust the altitude and azimuth, the redundant done button (vis a vis stop) has been removed.

Here is a screen shot: https://photos.app.goo.gl/HgSwb5kdFFgvxHyy8

• The white arrows indicating directions for alt/az correction, with size of the arrow related to the amount of correction needed (though it maxes out at 10').
• The algorithm selection pull-down (to the right of the refresh button) allows the new or old refresh scheme.
• In the new scheme a triangle overlay on the star-map is still used (showing correction progress) but since we're moving the center as opposed to moving stars across the triangle, it isn't as central to the UI.
• The LED panel shows the current polar-alignment phase.

This has been significantly tested on my telescope and is now ready for user testing.