Bug 1065650 - make job exclusion form validation more explicit

Also:
Move the exclusion name and description to the top of the form to
make it more prominent.
Change the max-height of the menu bar panels to avoid long scrolling.
Fix sort order in the job exclusions options
Add a back button to the job exclusion form
Merge pull request #168 from mozilla/bug-1065650-job-exclusion-validation-error

make job exclusion form validation more explicit