Expired tiles are not reloaded

[alasram]

Describe the bug
Tiles with short lifespan are not reloaded (example: weather tiles that are changing every seconds, traffic data that are changing every 3 seconds...).
The lifetime is is set as a max-age HTTP Cache-Control.
When the tile is loaded the expiration information max-age is set in mbgl::Response::expires.
The response expiration will eventually flow to the Tile in mbgl::Tile::expires. The value stored in mbgl::Tile::expires is only used in the debug visualization. The tile cache and the algorithm that updates what tiles are retained do not use the expiration information.
The tile cache logic needs to be updated to consider the expiration information and to reload the tile if it expires. This should also triggers a rendering repaint when tiles are reloaded.