Allow admins to default user preferences in mirth.properties #322

From #279 (comment)

User preferences must always be configurable by each user. Admins should be able to set different defaults for user preferences in a properties file.

Extend mirth.properties to allow admins to override user preference defaults from the code. The order of operations should be:

• user preference from each user
• admin default from properties
• hardcoded default from code