Use UTF-8 encoding on Windows

Summary:
Added an advanced CMake option MITK_UTF8 (default: ON) to the MITK build.
If enabled, a manifest file is embedded into all MITK applications to
switch to the UTF-8 code page introduced in Windows 10 Version 1903.

It finally solves some issues with characters like German Umlauts in
file names and eases cross-platform development, since both Linux and
macOS are based on UTF-8 as well.

Prevent unnecessary UTF-8 conversions

No need to convert anything if the source and target code pages are equal.

Fixes T28285.

Test Plan:

• Save data with German Umlauts in the filename
• Use such characters in the application itself
• Open a DICOM file with an German Umlaut in its filename
• Unit tests

Reviewers: floca, O1 MITK Reviewer Group I

Reviewed By: floca, O1 MITK Reviewer Group I

Maniphest Tasks: T28285

Differential Revision: https://phabricator.mitk.org/D653