Define content type for activity details to allow for intelligent rendering of data

Currently we store different formats of data in the activity details column (text, html). We are also planning on storing json-encoded data for the 4.1 release. Pages which display this data need an easy way to determine the content type in order to display it in a readable manner. Use internet media types as the option values ("text/plain", "text/html", "application/json" are the options we'll use for now).

1. New column for civicrm_activity

• content_type VARCHAR

2. Upgrade

• insert new column
• update existing activity records and assign either "text/plain" or "text/html" depending on whether HTML tags are present in the data

3. Send Email / CiviMail

• Assign appropriate content_type to inserted activities

4. Change case custom data - insert activity (http://issues.civicrm.org/jira/browse/CRM-8508)

• Assign content_type = "application/json"

5. View Activity

• Surround 'Details' display with <pre> </pre> tags if content_type is NOT text/html.