Autoload the detected and usable caching engines in the admin panel

Signed-off-by: emanuele <emanuele45@gmail.com>
Caching classes should add their own settings

Signed-off-by: emanuele <emanuele45@gmail.com>
Add bits of stuff to the "prepare_file" to make it similar to "prepare_db" (they should really be a single thinction I think)

Signed-off-by: emanuele <emanuele45@gmail.com>
And finally make the toggle works with javascript, so that the settings page shows only what is necessary for each engine

Signed-off-by: emanuele <emanuele45@gmail.com>
Removed deprecation notices (too much noise) and some other doc added

Signed-off-by: emanuele <emanuele45@gmail.com>