[Enhancement] non-latin glyph support via multiple TrueTypeFont files simultaneously #1613

Finding glyphs
lms has support to show non-latin glyphs on Squeezeboxes with a display via loading of one TrueTypeFont file. While this is already really nice, there are two minor issues with the current implementation:

1. Most font files only cover a set of glyphs, so you need to find a font file that covers all glyphs one cares about. Ideally multiple fonts should be tried (in some order) to find the glyph. Often enough font files are already installed on ones system.
2. lms treats the font file as an extension of the latin bmp files by name of the bmp. Which means that if you use a plugin to change the font for the latin glyphs, the non-latin glyphs don't get shown while using that font.

Expected behavior
In the perfect world lms would display any glyph perfectly on the Squeezebox without any action from the user, regardless of which bitmap font is chosen. As that's clearly too much to ask for, I can come up with several alternatives for point 1) above:

1. lms searches common places in the operating system and uses any font file that is able to display a missing glyph from the bmp file without user interaction.
2. Same as 1) but with the option to choice the order in which font files are searched for the missing glyph, e.g. via a drop down menu.
3. Enable the user to provide an ordered list of paths to font files in searching order.

Maybe a user would want to use a font from a font file even for the latin glyphs.

System Information (please complete the following information):

• OS on which you're running LMS: Debian testing/forky
• Hardware on which you're running LMS: x86_64
• Web skin used: Default
• Browser: Firefox
• LMS Version: 9.1.1
• Player(s) involved: Squeezebox Classic and Squeezebox Receiver