Add .clang-format file
Summary:
Reformat Core
Adding a .clang-format file and reformatting the core to comply to its guidelines
Test Plan: Dashboard
Reviewers: O1 MITK Core, kislinsk
Reviewed By: O1 MITK Core, kislinsk
Subscribers: kislinsk
Maniphest Tasks: T19210
Differential Revision: https://phabricator.mitk.org/D12