Obfuscate URL IDs - Githubissues

Overview

Improve URL navigation by obfuscating IDs with friendly slugs.

Fixes #50

Install Friendly ID
Set up Friendly ID for Data sets, users, and unique values (call types)
Add redirect logic to handle slug changing (only for data sets since users and unique values slug should not change)
Adjust the CallTypesController to have a new show action in order to make a specific call type accessible by URL (for sharing, discussing, etc.)
Update CallTypesController#index to redirect to the show action once a call type has been picked
Update the redirect logic once a user has classified all call types for a given data set. The app will now redirect the user to the data sets list with a notice to let them know they have classified all call types for that data set.
Update the classification paths to use the unique_value instead of the data_set
Add missing timestamps to the unique_values table
Add a new state to the classification page. When a user has already classified a call type, they will still be able to access it but won't be able to classify it again. See screenshot in Notes below.
Fix all specs to work with the new approach.

classified

All existing data sets, users, and unique values need to be re-saved to generate a slug:

DataSet.find_each(&:save)
User.find_each(&:save)
UniqueValue.find_each(&:save)