CORE-636 List of attributes for each type in AD
Merge pull request #2061 from reciprocity/epics/custom-attributes-admin-dashboard

CORE-636 List of attributes for each type in AD
Intermediate work on linking customattributables and customattributevalues.
Merge branch 'epics/custom-attributes' into feature/custom-attribute-search

Conflicts:
	src/ggrc/assets/javascripts/models/custom_attributes.js

Also, correct relation between CustomAttributable and CustomAttributeValues.