Improve the Advance Help Documentation: filter section

Detail description:
add explanation about rearrange icon, group operator, exposed filter and override info

I improve the whole documentation for the new views3 development. I arranged with dereine that i will upload the changes as single commits. Sadly i have already made all the changes in the documentation, so i have to split them. I will upload the pieces the next day one by one.
I am glad to get Feedback.

In the end i will upload a new views.help.ini with the better structure.