Refactoring: DataFrameWidget(QWidget) -> DataFrameWidget(QTableView)
I think that deriving DataFrameWidget from the QTableView is more logical than from QWidget

did you open 2 PR's fro this? #7021, #7020 pls close one of them

here are some git tips: https://github.com/pydata/pandas/wiki/Using-Git
 Nope. I don't know why but when I did `git pull-request` via GitHub `hub` tool it copied the old message. In this pull request I refactoried some code.

Or I should wait until my first PR will be accepted? I'm not an expert in git yet...
 ok, before you go further we need to create a test structure. That is important to retain backward compatibility.
 I agree with you but I need to submit labs in mathematical modeling :smiley: So I'll write my code. When someone would get ideas how to unit test PyQt application I'll add tests.
 https://github.com/ChrisBeaumont/qt-travis-test
 OK, I'll try it later. I don't know how to deal with constantly changing version of PyQt. May be we should just install PyQt from repositories? I don't know how does Travis work but I think it should be possible. Other problem is: PySide, PyQt4 and PyQt5 should not be mixed. I don't know how to make several build environments.
 they can be done on different builds. All I need are instruction to install from repositories and/or pip.
 need tests for these, maybe should be taken out of pandas
