SPAT Timestamp - Latest

[jacob6838]

This PR adds the latest query param to the /spat/json endpoint, and incorporates it into the GUI. The changes are as follows:

• API - added latest query params to /spat/json, which grabs the latest SPAT message
• API - added compact query params to /spat/json, which reduces the size of SPAT data in responses by eliminating "duplicate" messages
• GUI - When map is loaded without context (no notification/timestamp), it retrieves the latest SPAT data timestamp through /spat/json?latest=true, and re-renders the map with that timestamp

Note: The compact functionality is not yet integrated into the GUI, this is not yet supported. This will be completed in a future PR.

[jacob6838]

The map will now auto-select the latest SPAT message and re-render with that timestamp:

[John-Wiens]

Compaction doesn't provide SPaT deduplication. Currently is just removes the validation messages field. Since this field is very verbose, this reduces the required bandwidth for transmitting SPaT messages considerably.