Expose Dock/ Float for windows to Python

[NickDraper]

My instrument view is large enough so that I want to as a default kick it out of the tiny dark grey window in MantidPlot. I am preparing a script for users that would do this automatically, and would like to use this script to change a window to ‘floating.’ This feature can be done from using mantidplot, windows menu, change to floating, but I’d rather this be done automatically, regardless of user settings on MantidPlot, for ease of use.

I think we want something like the following on all mdisubwindows:

• float()
• isFloating()
• dock()
• isDocked()

[NickDraper]

This issue was originally trac ticket 9060