Make customer name in panel a link to that customer.

Closes #10
Added importance integer for customers.

This shows as a label on the customer panel.
Completed importance for customers.

Added importance to form and validation for only integers. Finally, added importance to the allowed parameters in the customers controller.

Closes #6
Add active boolean for customers.

Also added a checkbox to the customers form for this attribute.

Closes #2
Using #2, only use active customers on navbar dropdown.

Selecting all customers will still show active and inactive customers.
Merge pull request #20 from matthew-parlette/customer_improvements

Customer improvements