refactor(app): Simplify subgenerator code

Add a common function in the base script to simplify the common tasks
for many of the generators (services, filter, directive, controller).
Also remove some unused modules from the sub-generators (path and angularUtils).

Basically, I moved a lot of duplicated code to a common function in the base script. Since many of the sub-generators use the same pattern (add Source, add Test, add to index.html), a good chunk of code was duplicated across the generators. A common function in the base script covers this nicely and simplifies the sub-generators a good deal.

No need to update tests or documentation, since it's a purely internal change.