Fix several converter issues

* add Process to Control import/export [story:46058165]
* prevent LinkPeopleHandler from throwing an exception on invalid format
# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.
# On branch canary
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#	modified:   app/converters/base_row_converter.rb
#	modified:   app/converters/controls_converter.rb
#	modified:   app/views/directives/import_controls_result.haml
#
# Untracked files:
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#	CONFIG_VARS
#	DATABASE_MEETING.md
#	Guardfile
#	app/controllers/search_controller.rb
#	app/converters/requests_converter.rb
#	backup/
#	check_slugs.rb
#	commit-message
#	data/
#	db/seeds.yaml
#	old/
#	spec/converters/
#	spec/fixtures/sections-with-illegal-data.csv
#	spec/fixtures/sections-with-illegal-metadata.csv
#	spec/fixtures/sections-with-legal-data.csv
#	spec/import_spec_helper.rb
#	ssl/
#	temp.diff
Fix minor import issues

* ensure original reference cell data displays on error
* fix restrictions on Person cell format
Add better error message for invalid reference cell formats [story:43686275]
Merge remote-tracking branch 'github/canary'