Allow captions to be completely hidden.

Often it's desirable to completely hide the captions. Right now the only way to achieve this is to go and manually clean them photo by photo (not ideal and tedious).

An alternative would be to allow the cleaning on import, but surely that's not ideal either.

So at the end, I did this small hack that adds a new setting to the "caption position" setting, with value "hide" and that causes all the captions to be 100% hidden (without losing them).

For your consideration, ciao :-)