Precompile handlebars templates

This is a quick proof of concept for issue #233. It uses the same basic technique for precompiling as other handlebars plugins for `require.js`.

As expected it is faster, shaving about 3 seconds off the test suite on my machine. Unfortunately it does increase the build size by approximately 50kB.  In theory this could be partially offset by switching the built version over to using the `handlebars.runtime.js` file. However, that would preclude the possibility of using templates in UI, unless they are also precompiled. Templates in the UI could prove very useful for things like validator results.

This is a user-invisible change so no documentation update is needed. Furthermore it has negligible impact on the build process.