Add some of the additional GitHub files

.github/CONTRIBUTING.md

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+## How to contribute
+The easiest way to contribute is through a separate fork of the repository and submitting a pull-request. One of the core developers will judge the pull request and integrate it into the main `master` branch. Preferably, there is an accompanying issue (created by you or not) which is solved by the PR. In this case, feel free to use the phrase "(closes #XXX)" in the text of the pull request, where `XXX` is the number of the issue that you have solved. The PR should be in its own separate branch following the naming `pr/feature`, where `feature` is a short, descripting name of the additional feature or bug contained in the PR.
+
+For more information we refer to the [Wiki](https://openspace.github.io). If there are any questions, feel free to contact us via [email](mailto:mail@alexanderbock.eu?subject=OpenSpace: Contributing).

.github/ISSUE_TEMPLATE.md

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+<< Description of the problem >>
+
+<< What did you expect to happen >>
+<< What did happen? >>
+
+
+<< Attach screenshots, if possible >>