chore(gulp): add dev and test tasks
feat(example): add stylesheet to example
fix(tests): add KARMA_BASE global constant to prefix the files requirements

This is mostly just to fix the error shown by WebStorm.
chore(pagination): rename static mixInto to extend

I am still on the fence on which is the best name for the method, but if we consider that mixins are basically multiple extensions, and when declaring a class you use the keyword "extends" it makes sense that Pagination is extending the given instance.
chore(pagination): refactor most attributes into properties and add watchers