Fixes XNAT-2874: Added date validation to add experiment pages. Hide "NULL" text from note field.
XNAT-2874: Remove Date Message and Image if we are returning true.
Fixes XNAT-2902: Display error and fail validation if experiment id already exists.
XNAT-2904 Changed when welcome emails are sent during verification process to no longer erroneously send before user is enabled.
XNAT-2850: Added check in maven.xml to not build tip.txt if the Mercurial repository doesn't exist. Cleaned up code around different version algorithms. Added check for non-existent tip.txt.