Allows blank units when editing DataSets.

[#42158297]
Returning nil instead of '' in to_hash
WIP on multiple choice choices
Deleting obsolete runtime files
auto_actions :all in MultipleChoiceChoice controller

This allows an edit link for the choice to work. [#29126947]
Leaving these fields out of field_list in DataSet made all the tests break.
Update user activation email [#41045219]
Text changes to preview links, breadcrumbs

[#38526783]
Added page numbers in semantic json, [34208901]
updated the json for Page numbering. [34208901]
Updating runtime in hobo for [#42212947]
Merge branch 'master' of github.com:concord-consortium/smartgraphs-authoring
Cleaning up old runtime builds
Merge branch 'master' into staging