Dax

-Fix XnatDemographic
-Fix override of processor suffix in project settings file
-Fix Xnatupload delete all option

dax launch/update: better handling of projects that have modules but no processors

Bug fixes including:
-dax build: better handling of empty inputs field
-Xnatdownload: fix deleteall option
-dax build: ony run Module.afterrun once per session instead of every subject
-dax build/update: handle projects with no processors
-dax build: catch errors and email admin, specifically errors in yaml settings file
-XnatSwitchProcessStatus: handle multiple assessors
-XnatReportAssessors: more columns
-xnat datatypes: fixes for XNAT 1.7.5.6
-docs: updates for readthedocs

-Freeze pyxnat version
-Bugfix for Xnatupload

Fixes bug causing dax_version_hash to be blank.

Performance improvements for dax build