More consistent controls

[feross]

Tried to match the YouTube player UI more closely. There's still work to do, but this is a huge improvement for consistency:

Compare to:

• Increased size of all controls
• All buttons consistently get lighter on hover, without redundant css
• Play button moves to left, just like YouTube
• Time tweaks: thinner font, less verbose (0:xx instead of 00:xx, and omit hours when they're 0)
• Bigger volume slider nub
• Show back/forward buttons in top left on Windows/Linux, when in player
  • So it's consistent with OS X version, and the back button doesn't move around
  • Also, there are technically situations in which the forward button is needed from the player
    • Like if you start creating a torrent from the player, then go back, then want to go forward again
  • Make the background of the header bar transparent since it's mostly empty and looks terrible otherwise

This is what it looks like on Windows:

[dcposch]

LGTM!

the other changes are really subtle, but putting the play button on the far left definitely feels cleaner

also, nice job aligning it with the back arrow, that looks pro