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

• https://github.com/mgcrea/angular-pull-to-refresh/commit/a0a1dac6a85aa0c46564bf8db4b113b48e044f2e https://github.com/mgcrea/angular-pull-to-refresh/commit/1c89d5134882b135ece14844de94a7d9787ed1bc add attribute pull-to-refresh-config, with a test included (should solve the issue I've created https://github.com/mgcrea/angular-pull-to-refresh/issues/18)
• https://github.com/mgcrea/angular-pull-to-refresh/commit/061d6e29152f76842b477c6d409db65812a52f04 add new demo with files hosted on github (before doing this I was struggling with a way of easy test it in different devices)
• https://github.com/mgcrea/angular-pull-to-refresh/commit/f3085f2a96949b55a55efc0e80e94c2f23bb1e9d https://github.com/mgcrea/angular-pull-to-refresh/commit/94ab429488e9ab756e7e320b97e5647f90bdee1c https://github.com/mgcrea/angular-pull-to-refresh/commit/512b20710d520844b418cbc877ad7193c0f6ba6e 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 https://github.com/mgcrea/angular-pull-to-refresh/issues/9)
• https://github.com/mgcrea/angular-pull-to-refresh/commit/311da53f554a9c4012c49516faf8e5371f17ce4f change a little bit the readme file, I hope this improves the documentation (should help https://github.com/mgcrea/angular-pull-to-refresh/issues/12). Also added tested devices (https://github.com/mgcrea/angular-pull-to-refresh/issues/9 also working on android https://github.com/mgcrea/angular-pull-to-refresh/issues/4)
• https://github.com/mgcrea/angular-pull-to-refresh/commit/574ee947bd432e96f155e58a845ee9e710fc44d5 add optional dependency $translate (I need it in my App)
• https://github.com/mgcrea/angular-pull-to-refresh/commit/129badbfa8f4c48a32f77bb1dd1f023e6604577e https://github.com/mgcrea/angular-pull-to-refresh/commit/129badbfa8f4c48a32f77bb1dd1f023e6604577e 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.