Observation fixes and improvements

[JustinElms]

Background

Mostly minor improvements to observation components:

• Improved observation track data processing to reduce endpoint response time.
• Made track colors consistent with point observations.
• Cleaned up point observation data selectors - removed irrelevant dropdowns.
• Modernized some obs DB queries.
• Clear previous observations from map when selection is updated.

Checks

• I ran unit tests.
• I've tested the relevant changes from a user POV.
• I've formatted my Python code using black ..