Make global error template user customizable

[kevsmith]

Overview

We've gotten several requests to make the error template user customizable. Emerging community consensus is the default error template is great for developers but contains too much information for non-technical users.

Requirements

1. Cog admins must be able to revert back to the default template at any time.
2. Template customizations must persist across Cog restarts.
3. Documentation of the customization process, including a list of available variables, must be part of the doneness criteria.

Constraints

1. A global customized error template is good enough for now.

[mpeck]

Proposal

I think we can solve the problem by providing a config option that specifies a path to the error template on the machine running Cog. During startup we check for the config option and replace the standard error template in the db if it is set. Vice versa if it isn't set we just set the error template to the standard one.

This shouldn't require too many changes. When Cog starts we refresh common bundles. We can intercept that call and replace the standard error template with a new one defined by the error template config option. By unsetting the option and restarting Cog, the template should return to the original naturally.

• Add custom error template path config option
• Update Cog.Repository.Templates.refresh_common_templates!/0
• documentation