Add template pre-caching

[stackfull]

Not sure this is necessary as the html loader is good for templates.

[jeffling]

it could be good to reduce bundle size, ie. load the first template the user hits into the bundle, precache the rest after the first page is already rendered.

It might also be able just to use normal webpack lazy-load syntax... but I haven't tried that yet.

[scottmas]

You're right, html-loader does work for almost all cases. However, it would be nice for this plugin to have a story for when developers use ng-include to fetch external html fragments (and webpack would not by default put these html fragments in the bundle directory) or when they want to specify a templateUrl rather than template in their router or directives. This said, its still probably not a big deal.