fix(ui): Use *-symbolic variant of toolbar icons

[moetayuko]

The non-symbolic variant might be indistinguishable from the background.

Fixes #34
Ref: https://wiki.gnome.org/Design/OS/SymbolicIcons

Before

GTK_THEME=Materia swappy -f foo.png:

GTK_THEME=Materia-light swappy -f foo.png:

GTK_THEME=Materia-dark swappy -f foo.png:

After

GTK_THEME=Materia swappy -f foo.png:

GTK_THEME=Materia-light swappy -f foo.png:

GTK_THEME=Materia-dark swappy -f foo.png:

[jtheoof]

Interestingly I don't have the problem without the patch, but multiple people have reported the issue. I think the patch makes sense.

@moetayuko Can you just fix the commit message, commitlint complains about the use of Capital "Use" instead of "use". Sorry it's a bit intense, but for good reasons. :)

[moetayuko]

Interestingly I don't have the problem without the patch, but multiple people have reported the issue. I think the patch makes sense.

Dunno, might be relevant to the gtk theme and icon theme in use.

@moetayuko Can you just fix the commit message, commitlint complains about the use of Capital "Use" instead of "use". Sorry it's a bit intense, but for good reasons. :)

Should be fine now.