Mantaflow "replay" mode change

Right now, the Mantaflow replay type cache is nearly useless. Worse it promises what we had before and fails to deliver. Replay should work like other baking in blender. When you first start playing your animation with replay mode, it should show a progress bar in the timeline which displays the currently baked frames. If you move any part of the simulation or change any parameters, that bar should disappear and the cache should be cleared. There should be a "free cache" button as well. This would make it much more clear what is happening and save some grief.