2021-February-07 - Prerelease - 2.6.49@3ce726c3de

Update download modules to use 'map.yml' to determine map names (#8798)

Numerous fixes required for downloads to work properly:

- Update downloads to find maps using 'map.yml' instead of doing folder name searches

- Move unzip operation earlier in map download. Before generating a missing 'map.yml'
  file, we need the map to be unzipped.

- Generate missing map.yml files on startup and not just when selecting games. The download
  maps windows needs a full index of map.yml files.

- Normalize map name matching. This is important as the value in 'map.yml' may not
  match the human readable version obtained in the download list.

- When generating a map.yml file, use the name of the map folder rather than 'mapName'
  property from XML. The 'XML' property can be incorrect for the case of 'old variants'
  that use a map name that does not match the installation folder.

- Generate and assume 'map.yml' file will be at map top level folder. This makes it easier
  to find the maps top level folder.

- Move downloaded map delete logic to DownloadFileDescription, improves data encapsulation
  (and specifically better encapsulates how we find map files based on map name)