Add filters to only show class under length

[yringler]

Something which would help people find a class which fits into their schedule...
Have a filter so they only see classes of the right length

1. Global way to add/remove filter
2. In a section, if we are hiding classes based on filter, there should be a view more button to show all classes in that section (just for that screen - if user goes back and forth, wouldn't be remembered)