Grails json-views: Make templates easier to debug and use

[rmorrise]

I find troubleshooting json-views extremely difficult. Here are some (hopefully small) concrete changes that would really improve the experience:

• Add TRACE- or DEBUG-level logging to the template resolver logic. The log output should show which paths were tested and whether or not a template was found.
• When invoking tmpl."/templateType/_templateType", the template resolver is converting it to a double-underscore: /templateType/__templateType. The framework should not do this.
• Make sure all code paths attempt to use the template resolver. It seems like it doesn't always try to resolve templates for non-GORM objects.
• I don't know why, but it keeps trying to resolve templates for java.lang.Long. It doesn't seem to do this for other built-in classes (like strings). This doesn't really hurt anything, but it makes debugging take longer.
• Document the behavior for absolute VS relative template URIs
• Document an example of rendering an array of items using parent and child templates (master-detail)

[jameskleeh]

• OK
• That is documented http://views.grails.org/latest/#_templates
• OK
• Sounds like a bug
• That is documented http://views.grails.org/latest/#_templates. Perhaps it could be made more clear
• Pretty sure that is documented as well. You'd have to provide an example of what you mean.

A PR would be welcome for any of these improvements