Unicode icons: Triangles for up and down sorts

[johnwdubois]

Is your feature request related to a problem?
The icons for sort direction are hard to read when they're small.
Use a simpler, cleaner, sharper icon. (Avoid pixelation and feathered edges.)

Describe the solution you'd like

1. Use Unicode characters for icons whenever possible. They're simple, and should look sharp and easy to read at almost any size.
2. For up and down sort directions, use the following Unicode characters. Choose the size (large or small) based on what works and looks good (large version if possible).
3. Down/active: 'BLACK DOWN-POINTING TRIANGLE' (U+25BC) or 'BLACK DOWN-POINTING SMALL TRIANGLE' (U+25BE)
4. Down/inactive: 'WHITE DOWN-POINTING TRIANGLE' (U+25BD) or 'WHITE DOWN-POINTING SMALL TRIANGLE' (U+25BF)
5. Up/active: 'BLACK UP-POINTING TRIANGLE' (U+25B2) or 'BLACK UP-POINTING SMALL TRIANGLE' (U+25B4)
6. Up/inactive: 'WHITE UP-POINTING TRIANGLE' (U+25B3) or 'WHITE UP-POINTING SMALL TRIANGLE' (U+25B5)
7. Forward/active: 'BLACK RIGHT-POINTING POINTER' (U+25BA) or 'BLACK RIGHT-POINTING SMALL TRIANGLE' (U+25B8)
8. Forward/inactive: 'WHITE RIGHT-POINTING POINTER' (U+25BB) or 'WHITE RIGHT-POINTING SMALL TRIANGLE' (U+25B9)
9. Reverse/active: 'BLACK LEFT-POINTING POINTER' (U+25C4) or 'BLACK LEFT-POINTING SMALL TRIANGLE' (U+25C2)
10. Reverse/inactive: 'WHITE LEFT-POINTING POINTER' (U+25C5) or 'WHITE LEFT-POINTING SMALL TRIANGLE' (U+25C3)

Describe alternatives you've considered
Using hand-made sprites does give more control over Rezonator design. But for practical reasons, including legibility, the use of Unicode characters seems preferable.
On the other hand, if the user's fonts lack the Unicode character, this could be a problem. This is part of why we use Noto Sans. Also, I think the triangle characters are pretty widely supported.

Addtional Context
Go to the Rezonator wiki page on Icons.
See also Unicode.
See also #126 .