Add support for TDoA 3

[krichardsson]

The new TDoA 3 positioning mode in the LPS system supports a dynamic number of anchors. Some rework is required for the LPS tab to support this.

1. Handle positions for a dynamic number of anchors
2. Handle status for a dynamic number of anchors
3. Move anchor position configuration into a separate dialog and handle a dynamic number of anchors
4. Add functionality to change the positioning mode to TDoA3 in the CF
5. Add functionality to change the positioning system mode to TDoA3

[krichardsson]

Related to bitcraze/crazyflie-firmware#366 and bitcraze/lps-node-firmware#40