Scope filters to pending submission column.

Fixes #417 introduced by 7ba9455423ccec44dfd5b6c69668cce162117d3e
The tooltips added in the above commit added data attributes to elements
that were being used to filter. This scopes the filters to only act on
the main content div of the submissions page.
Merge pull request #417 from kytrinyx/hotfix/too-much-filter

Pending screen does not show pending exercises, HTML tag has display:none