Allow .otf as a valid file extension, too. 

While it is not documented, AnkiDroid works fine with `otf` fonts.
Only it stopped loading them: 1cae6b8c79960d0d67ec3552774778b1ad0d59af

So, do load them again, but use an Array. Like this, it is easier to add other font file formats that may work as well.

This also loads files with uppercase file endings `.TTF` again...