Task T26840-MitkHomepageReorganization-TopLevel-integrationBranch

Summary:
Several commits, all changing the top level documentation of MITK documentation webpage.
Mostly, deprecated files are deleted, or labels renamed to ease the reading. The structure is more
slim now. Note: 1) During building of the doc, still errors occur. Those do not hinder the creation
of the documentation, however, should be fixed in the future. Some commits already solve those build
errors but not all of them could be eliminated yet. 2) Two more files need to be modified
but since they contain invalid UTF8 sequences, arc cannot handle them correctly. The need to be
merged without arc.

Test Plan: Validate webpage

Reviewers: O3 MITK Reviewer Group II, O1 MITK Reviewer Group I, kislinsk

Reviewed By: O3 MITK Reviewer Group II, O1 MITK Reviewer Group I, kislinsk

Subscribers: thomass, kompan

Differential Revision: https://phabricator.mitk.org/D356