Fix PNGs with incorrect color profile.

> convert plover/assets/connected.png plover/assets/connected.png
convert: iCCP: known incorrect sRGB profile `plover/assets/connected.png' @ warning/png.c/MagickPNGWarningHandler/1830.

> convert plover/assets/disconnected.png plover/assets/disconnected.png
convert: iCCP: known incorrect sRGB profile `plover/assets/disconnected.png' @ warning/png.c/MagickPNGWarningHandler/1830.
Merge pull request #111 from benoit-pierre/fix-bad-pngs

Fix PNGs with incorrect color profile.
Improve X11 keyboard emulation.

Make sure every key event time is different than the previous one, to
avoid some applications thinking its an auto-repeat.