Make align system more dynamic and user-friendly

[brickbots]

Based on great feedback from @mrosseel this is a PR to polish up the Align feature:

• Use IMU updated camera center position for chart while not in star selection mode
• Allow zoom in/out when in star selection mode
• Use standard reticle to indicate current alignment point before entering star select mode
• Provide prompts along the bottom of the screen to indicate next steps

I tried to use the IMU during the entire process, but it made it much more confusing as the selection point would move to the star's location when the arrow was pressed, but this would almost alwasys be a little different in the next moment due to the imu motion from interacting with the PiFinder. This would make it seem like it was not selecting the star, but was slightly offset. Tying the location to the camera solve during star selection makes for a nicer experience as the selected star is well indicated and the set of stars is stable for selection.

To help guide the process and avoid user confusion, the chart starts dynamic using the IMU and shows the current alignment using the normal reticle pattern. A prompt is displayed along the bottom to guide the user through and should, hopefully, make the process more understandable.