Fix javascript loading bug

[smcalilly]

Overview

• closes #273

The extra_js template block was loaded within another block. This caused all of the page's JavaScript to load twice, which crashed the javascript.

Testing Instructions

• visit this project: https://ccfp-asset-d-patch-asse-ssgn33.herokuapp.com/projects/428/
• login as username=test and password=supersecret
• use the pagination for the assets table, make sure it works