Escape output from mark_helper

[crowesn]

Fixes #950

User submitted html source code is making it into our public display.

Changes proposed in this pull request:

• Remove html_safe from mark_helper0
• Add spec

[crowesn]

Running bisect on these failures.

[crowesn]

Bisect complete! Reduced necessary non-failing examples from 1773 to 27 in 446 minutes 53 seconds.

The minimal reproduction command is:
  rspec './spec/features/collection_export_spec.rb[1:2:1:1]' './spec/features/hyrax/collection_multi_membership_spec.rb[1:3:1:1]' './spec/features/hyrax/dashboard/collection_spec.rb[1:8:1,1:9:2:1]' './spec/features/work_show_spec.rb[1:2:1:2,1:3:1:1]' './spec/models/dataset_spec.rb[1:2:1,1:4:1,1:4:7,1:4:11,1:4:12,1:4:16,1:4:17,1:6:3:2,1:6:3:3,1:6:3:7,1:6:3:9,1:6:3:10,1:6:3:13:2:1:1:1:1,1:6:3:13:2:1:1:3,1:6:3:13:2:1:3:1:1:1,1:6:3:13:2:1:3:2:2,1:6:3:13:2:1:3:2:3]' './spec/models/document_spec.rb[1:7:3:5,1:7:3:6,1:7:3:9]' './spec/models/medium_spec.rb[1:7:3:5]' './spec/models/work_and_file_index_spec.rb[1:4:2:2]' --seed 19422

[hortongn]

@crowesn I'm having problems running the specs on your branch, but I noticed that your branch is stale and missing many commits from the last several months. Please rebase and let's see if CI likes it better. I'll try again then too.

[crowesn]

I think this should be ready to go -