chore(*): introduce additional scopes for testing different AJS versions

Example usage: ```TEST_SCOPE=angular_1.3.x grunt test``` runs all tests against latest AJS 1.3 release

Run `grunt install-test` to ensure all scopes' dependencies are fully available.

More commands:
* `npm run-script test-scopes` runs all available scopes (entries in `test_scopes/`)

Adding new scopes (or remove it again):
* Check entries in .gitignore, .npmignore
* Add directory in test_scopes with a bower.json
* Add matrix build in .travis.yaml
docs(loader): add guide (de, en)