Fixes issue with autoprefixing.

Autoprefixing and Sass processing were being done in the wrong order. (Also adds prefixing support for Safari 8.)

Also adds Watch flag for changes to all Sass files.
Adds sticky positioning to alphabetical indices.
Improves the way content and sidebar interact.

Also improves how sticky positioning works in these content divisions.
Fixes flexbox layout bug in IE 10.

Removes -webkit prefixes for flexbox, because it's now handled by (and can get in the way of) Autoprefixer.