Don’t abort when user cancels “Documentation for Property”

Using abort will show an error dialog in TextMate 2.

Closes textmate/textmate#900.
"Documentation for Property" now works for (most) CSS3 properties.

Unfortunately there is no "official" compound index of all CSS3 properties. There are several unoffical indexes, the updated list of properties in the bundle is generated from http://meiert.com/en/indices/css-properties/ (provided by Jens Meiert; seems fairly complete and up-to-date).
Make 'Documentation for Property' also work in source.scss scope.