375 job management

[mradamcox]

Adds a new job management system to the platform, to close out #375 . On drafting this pull request there are still a handful of smallish changes I want to make before considering this completed.

• Actually cascade everything from single COGs
  • It is much faster to create XYZ tilesets after a single COG has been created, so that's the only way it should be allowed
  • Will still need to retain separate dates, but stale xyz will be true when its date is older than the cog date
  • If a COG and XYZ tileset both exist, but then the masks are updated, then XYZ generation should not be enabled until the COG has been updated. I.e. you can't queue XYZ tileset for creation if the current COG is stale.
• Loading indicator when you switch to the Derivatives tab, it can take a moment for the layersets to load up
• Same for the multimask tab (not directly related to this task but may as well)
• Force the styles on disabled buttons to fix the issue that @jacobwhall encountered