Option of user-specified font

[rvighne]

Previously, users were limited to picking from a fixed list of font options.

This change allows the user to type in the name of any locally installed font. There is also an unobtrusive autocomplete dropdown to let them easily choose one of the fonts that ships with Sight.

[sschr15]

Until merged, I've found a workaround:

1. Inspect the config page (F12 or ctrl+shift+I, probably)
2. Change a non-selected element of your choice to be the font name within the value attribute
3. Select that from the dropdown
4. Repeat every time you enter the options