Upgrade FuelUX to 2.6.4

Note that the CSS file, Bootstrap, is the same as 2.6.0, so I just renamed it.
Fix: "Import" steps warns when users haven't selected/uploaded files

Previously, users could choose a file from their system but forget to upload it,
and the CWA would be fine. Now the CWA warns when there are files left in the
upload queue. I also added a warning when both the upload queue and list of
uploaded files are empty.

Closes #41
Remove the "scripts" directory

For quite a while, the WorkflowManager has automatically detected the path to
R bar chart script, meaning the CWA's local "scripts" directory is not only
the remnant of poor planning, but also no longer necessary. Yay!

Closes #18 and closes #34