Directive works in more cases than before and add some functionalities (see description)

[freefri]

First of all, sorry about 9 commits in a single pull request, but at the beginning, I was not thinking to make the PR but at the end I've changed my mind.

The changes

• a0a1dac 1c89d51 add attribute pull-to-refresh-config, with a test included (should solve the issue I've created Is there a way to make it work with glyphicon? #18)
• 061d6e2 add new demo with files hosted on github (before doing this I was struggling with a way of easy test it in different devices)
• f3085f2 94ab429 512b207 make it work and animate the "pull to refresh" using the JavaScript event. Native style momentum with overflow-scroll is not mandatory anymore (this may solve Neither demo nor plugin work on any device #9)
• 311da53 change a little bit the readme file, I hope this improves the documentation (should help how to use in straightly pull to refresh #12). Also added tested devices (Neither demo nor plugin work on any device #9 also working on android Does this work in Android? #4)
• 574ee94 add optional dependency $translate (I need it in my App)
• 129badb 129badb make the tests pass

I didn't extend much with the tests, because I think this stuff is hard to test, and I didn't want to expend much time.