Add cancel and back span helpers

[bmorrall]

Resolves #1120

Description

Adds a helper for "<< Back" and "<< Cancel" button and link labels. Some of these values were inconsistent or incorrectly (if not at all) escaped, this at least keeps things consistent and easy to repeat.

Guide questions:

• What motivated this change (if not already described in an issue)?
  • Desire to fix something on the internet somewhere/anywhere. Inconsistent text formatting once kicked my dog, couldn't stand by this time.
• What alternative solutions did you consider?
  • find-replace/gsub text inline in all erb files.
• What are the tradeoffs for your solution?
  • uses a extra method for something that could be hardcoded directly into the erb files.

List any dependencies that are required for this change. (gems, js libraries, etc.)

• None

Include anything else we should know about. -->

• Some libraries are a little out of date at the moment (nio4r), not willing to bump those without understanding the project more.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Open browser and visually verify text is present.