Issue 2565, take two: provide docking widget that allows to search, paste and run magic commands

This is continuation of PR #5649.
a. I have re-implemented the whole "all magics" menu to be a simple docking widget that allows search, paste and run magic commands.
b. Search text works as regular expression. It is applied only on magics of class selected by the combo.
c. Double clicking pastes the magic command into the command line. 

![1](https://cloud.githubusercontent.com/assets/2404104/2833893/9825fee4-cfd6-11e3-8d14-2c2c0c5c090c.gif)