This change fixes up some JS dependencies in the djblets package.json

for consistency and correctness:

jquery-ui was set to 1.13 here but 1.14 in Review Board, and Review

  Board was winning. This updates the Djblets dependency to match.
Backbone was set to 1.4.1 but 1.6.x in spina, and spina was winning.
We had a (very old) uglifyjs dependency listed here because they

  changed the package name. The actual uglifyjs that was present in

node_modules/.bin when doing Review Board builds was from

uglify-js coming from a different dependency.

This is all much more completely redone on the 7.1.x branch.
package-lock.json is also part of this change but was excluded here.

Installed npm packages.
Built static media.