excel: Rework code to import side-python file.

* Prepare for windows installer.
* cmdline: Add --excelrun.
* Rename wltp_runner --> WltpExcelRunner
* Replace (some) Flashbang with just `python`.
* Add WinPython_requirments.txt.
Replace (rest) Flashbang with just `python`.
cmdline, build: Use setup.py `console_scripts` for `wltpcmd`.

* excel: Create folder in --excel[run] cmdlines.
* cmd: Fix logging-level to `info`.
* wininst: Still postinstall script does not run!
* travis: apt-get python3-pil to fix 'multiprocessing' build fail.