ReleaseNotesGeneratorForm: add label with help text
ReleaseNotesGeneratorForm: fix line breaks in TextBox; add new lines to HTML code
ReleaseNotesGeneratorForm: HTML table: clipboard content can also be pasted as text (HTML code) to text editor; prepare for unit tests
update GitExtensionsTest submodule
ReleaseNotesGeneratorForm: make buttons more descriptive
ReleaseNotesGeneratorForm: refactoring
update submodule
Submodule GitExtensionsTest updated

Submodule GitExtensionsTest:
    > 3d05c92 - mark test explicit instead of ignored