Fix Tomita launcher for Windows

* Correct Tomita executable file name for Windows
* Set shell=True on Windows in subprocess.Popen()
Change CLI interface for different graph formats

Instead of the '-g' option (for drawing in GML) there is now the '-f' option
that stands for 'format' and accepts the format name as its argument, e.g.:

    east -f gml keyphrases graph ...

Supported formats now are 'gml' and 'edges' and can be extended in future.