Restyle the music player bar

The bar is rounded and a little taller, with a round orange play button
and a restart button that lights up orange under the mouse. The icons sit
inside their buttons with room around them, and are one colour, cropped to
their shape. Progress fills in orange, the volume slider gets a speaker
icon, and the buttons say their shortcut keys in their tooltips.

Buttons grow a little under the mouse and shrink while held down, and the
play button pops when it switches between play and pause. ButtonBounce
holds these animations so other buttons can use them too.

icons/restart_light_icon.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="28" height="28" viewBox="0 0 28 28">
+  <!-- reload_light_icon.svg mirrored, so the arrow turns back like a restart -->
+  <path fill="#f9f9f9" transform="translate(28 0) scale(-1 1)" d="M 12.273759,27.821814 C 8.301606,27.305128 4.6414458,25.025364 2.4172439,21.682595 -0.6740156,17.036719 -0.6987372,11.050866 2.3541959,6.4167276 6.4831292,0.1492961 14.7875,-1.7884148 21.095349,2.0437368 l 0.883303,0.5366251 0.09577,-0.6963111 c 0.07593,-0.5520493 0.198918,-0.7994615 0.593645,-1.1941885 0.682393,-0.6823936 1.29683,-0.7876518 2.135162,-0.3657721 1.11162,0.5594083 1.142977,0.6968977 1.099029,4.8188242 C 25.866598,8.48735 25.848168,8.714727 25.583585,9.075118 24.993194,9.879284 24.711316,9.931761 20.980939,9.931993 17.03905,9.932238 16.871859,9.891713 16.324094,8.803226 15.94065,8.041272 16.00249,7.4396205 16.528498,6.8144942 17.041282,6.2050862 17.302265,6.1106614 18.732442,6.0170974 l 1.29765,-0.084894 -0.711421,-0.4557502 C 16.407302,3.611373 12.42501,3.4754273 9.250891,5.1327637 6.9185825,6.3505563 5.186242,8.47902 4.3514391,11.152542 c -0.4596099,1.471937 -0.4596099,4.222979 0,5.694916 1.0532717,3.373185 3.4279179,5.747831 6.8011029,6.801103 0.874696,0.273122 1.291973,0.316826 2.983051,0.31243 1.791555,-0.0047 2.062404,-0.03855 3.050848,-0.381822 2.095349,-0.727675 4.004905,-2.225187 5.276499,-4.137935 0.712133,-1.071201 1.028577,-1.77101 1.500599,-3.318525 0.234713,-0.769505 0.466198,-1.242244 0.733848,-1.49867 0.768275,-0.736054 1.953395,-0.694987 2.67526,0.0927 0.56162,0.612834 0.678351,1.318164 0.398766,2.409492 -0.7664,2.991551 -3.210883,6.444937 -5.916304,8.35812 -2.688606,1.901292 -6.251776,2.77056 -9.58135,2.337459 z"/>
+</svg>