Add syntax highlighting styles & highlight threshold.

Previously, highlighting classes were being added to the DOM but had no CSS
so the user just saw black - a lot of CPU usage for nothing.

These styles now attractively and minimally style resposes so long as
they are below a certain threshold, as well as model schemas.

The highlightSizeThreshold fixes the long hang users would
see when large responses were returned.
Merge pull request #56 from STRML/syntaxHighlighting

Add syntax highlighting styles & highlight threshold.