Fix carnatic sloppy code

[alastair]

Lots of code was written quickly for the carnatic release. It works, but some of it is messy and there's lots of duplicated code that can be cleaned up.

Some places to start:

• main view search/filtering
• Code in carnatic models that should be shared in data with hindustani
• Hard-coding of carnatic specific items in the data module (e.g. the word concert)
• similar functions that do almost the same thing but are duplicated instead of having an argument
• Duplicate code in templates that should be split into {% include %}s
• Duplicate templatetags for carnatic and hindustani, but needing to name them different things
• Tests