Merge pull request #9 from sartmann/master

Diverse Änderungen
[FIX] plotting isotope distribution was broken
[RELEASE] v 2.3.1
[WEBSITE] cleanup
Merge remote-tracking branch 'sartman/master'
[FIX] removed default setting for package store
[FIX] added exception handling when loading emzed.ext or emzed.app
[RELEASE] v 2.3.2
Merge pull request #11 from sartmann/master

Docs: rescaled pictures in getting_started.rst