Modernise help library info

Hello, this is my first pull request ever so be cool..
I made the UI revamp of the old library info dialog, which should fix the issue: https://github.com/openscad/openscad/issues/919

- [x] show all the info direcly
- [x] window is larger
- [x] window is sizable
- [x] changed the title of the window to something more appropriate
- [x] improved lisibility with bold font

Before:
![libinfo_before](https://cloud.githubusercontent.com/assets/3892244/4266450/4144076e-3c7e-11e4-8f31-63a5fee5e67f.PNG)

After:
![libinfo_after](https://cloud.githubusercontent.com/assets/3892244/4266454/46a0713e-3c7e-11e4-8e90-8ef3bb3142e9.PNG)

I hope this is usefull :)