Expose font settings for crosshair coordinates

[0tkl]

Same as https://github.com/arch1t3cht/Aegisub/pull/145, just rephrase the commit message.

Stop hard-coding the font face and size of the crosshair coordinates (currently Verdana 12pt). Expose the options to the user and move the coordinates' current font settings to the default profile.

Developers need to be aware of the font size here ~~when Hi-DPI support is about to be migrated to TSTools~~ after Hi-DPI support is in master.