Add "interests" table for clubs and users

[bfbachmann]

• In order to suggest clubs to users and vice-versa we will need a table that stores interests.
• Interests should be short strings like "Hiking", "Programming" etc.
• The interests table should have only two columns for now:

id	name
0	Hiking
1	Gaming

• The values for the ID column will be inserted automatically by Postgres (take a look at how we do id fields for [other tables] (https://github.com/ubclaunchpad/bounce/blob/master/schema/schema.sql#L3))
• The values for the name column should be UNIQUE
• You'll need to modify schema/schema.sql to add the table to our database (make sure you run make migrate from outside your container when you've added the table)
• You'll need to create a file bounce/db/interests.py and add methods to insert and delete rows from the interests table you created (see users.py as an example of what you'll need to do)