Upgrade RTTB to ITK 5
Summary: Mostly renaming of deprecated names, as well as removing references to the RTTB_ITK5_SUPPORT option.
Test Plan: See if it builds without errors. If in combination with an eMITK build, change the GIT_TAG in RTToolbox.cmake to "feature/upgrade-to-ITK5" to use this version
Reviewers: floca, kislinsk
Reviewed By: floca
Differential Revision: https://phabricator.mitk.org/D617