Compile only prototype in dev mode

[raderio]

Hi.
Compilation time of Scala is slow, so it is for twirl.
It could be improved if in dev mode if it will be parsed/generated only function prototype(name and parameters) and imports, the body of function will be compiled only for specific page in runtime when is loaded, so it will compile only a few templates and it will be fast and in controller the call of template will be safe.
It could be added as an option.

In prod mode should be the same as it is now.

Thanks.