Additional alignment options for sources.

In response to: http://obsproject.com/forum/viewtopic.php?f=7&t=3175

Alignment options have been added to the sources context menu. Center options are now grouped below the original options. The move to x options are grouped below the center options.

These hotkeys are debatable. After some testing, I believe they are easy to get used to.
Center horizontally: Ctrl + Alt + C
Center vertically: Ctrl + Shift + C

These hotkeys should be intuitive for gamers. An alternative would be to use either Ctrl + Shift + arrows, or Ctrl + Alt + arrows.
Move source to left of canvas: Ctrl + A
Move source to top of canvas: Ctrl + W
Move source to right of canvas: Ctrl + D
Move source to bottom of canvas: Ctrl + S