Handle new CEST data correctly

Summary:
Modify parsing for different "ASCCONV BEGIN"

New data does not mark the relevant section simply with
"# ASCCONV BEGIN #" but with something like
"### ASCCONV BEGIN object=MrProtDataImpl@MrProtocolData version=51130001 ..."
so the parsing needs check for different strings.

Replace tab ("\t") in new CEST image data files

Test Plan: manual testing

Reviewers: floca

Reviewed By: floca

Subscribers: floca, kalali

Maniphest Tasks: T28958

Differential Revision: https://phabricator.mitk.org/D591