Bug 1054766 - (gaia-progress) Create a gaia-progress web component

https://bugzilla.mozilla.org/show_bug.cgi?id=1054766
Heh, this is due to the rotation. If there were no rotation it would be 15rem, but due to the 135 degree angle, I think this needs to be changed. If you have a better way of specifying this please let me know.