Lexical colorization/classification for template strings.

[DanielRosenwasser]

Follow up to #1744 but for TypeScript 1.5.

This PR adds lexical classification support for template strings in the absence of a syntactic classifier.

It will break in the presence of

• Nested template strings that span multiple lines.
• Nested expressions composed of curly braces, where the closing curly falls on the next line.

But otherwise it is a fairly good approximation.

[CyrusNajmabadi]

Comment the purpose of this parameter so that consumers of the LS know what they should pass and how hte classifiers interact