add support for modular file structure

This adds an option to use a modular file structure via options.useModulesStructure"
Not sure if we could have just added the file structure we used as well, but anyway it's more error-prone this way.

PS: I also added karma config to the test watch triggers
do you think it's better to use "/*global describe, it, before, beforeEach, after, afterEach, etc.. in each test file? 
it can be tiresome, but in the other hand putting it in globals might (rarely) lead to some false negatives.