Mjob password strength

This is a new pull request for #2048.

The commit from #2268 is cherry-picked, because it was based on an too old master branch (2 months ago).

Requires owncloud/3rdparty#20

Task list from #2268

- [ ] Load the script asynchronous (how can I get the path of the 3rdparty folder in JS?)
- [x] Make the UI nicer - I'd like [such a cool bar (scoll-down)](https://tech.dropbox.com/2012/04/zxcvbn-realistic-password-strength-estimation/) and when clicking on the (i) there should more info displayed (time to crack, entropy etc...) 
- [ ] Clean up the JS / HTML (maybe even make it a jQuery plugin so it's reusable) - is here any jQuery guru who wants to do this?

Current appearance:
![password-strength](https://f.cloud.github.com/assets/245432/462363/379efe06-b4a5-11e2-8be2-221e4260c517.png)

A textual rating is in the title attribute, so a hover will show it.

Tested with FF20 and Chromium 26. Can anybody test it with IE?

cc @Raydiation @raghunayyar @jancborchardt @Kondou-ger