Change project license to GPLv3

[nightvisi0n]

fixes #36

[nightvisi0n]

@sedrubal since you are the only contributor, please reply in #36 if the license change is ok for you.

[sedrubal]

I think adding a 16 lines comment in each file containing code is absolutely insane. Here you can see that GPL is obsolete and I would ignore this advise and don't add the comment.

[nightvisi0n]

According to https://www.gnu.org/licenses/gpl-faq.en.html#NoticeInSourceFile this is very important.

[sedrubal]

...but its not practicable. I'm ok with "# don't separate this from the repo..." or something like that but 16 lines containing "blablablabalbabla" is :weary:

[nightvisi0n]

@sedrubal would you be ok with sth like this instead of the "16 lines comment"?

__author__ = 'Julian Neureuther <dev@jneureuther.de>, \
              sedrubal <dev@sedrubal.de>'
__copyright__ = 'Copyright (C) 2016 The authors of dockgraph'
__license__ = 'GPLv3'

[sedrubal]

Yes :+1:

[nightvisi0n]

@sedrubal please review :wink:

[sedrubal]

ok, LGTM :+1: