Allow importing font file

[shiki-tm]

I could be wrong but I don't think you can really install a font on Android system, at least for most people it's not possible. But I know it is possible to do this in websites like ttu reader for example even on android:

Also I don't see a drop-down menu when clicking on the subtitle font setting, so I don't even know if any fonts are available for use. If we had a button to import a font file from the device this would be very beneficial for all Android users of the extension.