Merge filter and filter-having-keys

Both these functions involve filtering in/out data, so it makes sense to
have them in the same tab.

"Filter having keys" is not very clear. Hopefully the new descriptive
sentence ("For the following keys, filter out events that don't have
values") will be a little clearer to new users.
Clarify "Remove filtered" a little
Add remove item link to each value in a filter

Instead of only allowing the user to delete the last value, it's nice
to be able to delete any value in the list.

Style the remove button as a red '-', and add a green '+' to the add
button to make this clear.

Also, move the add button above the checkbox, so it's clear that it's
referring to the list of values, while the checkbox is referring to the
whole filter.
Add remove item link to filter_having_keys
Rename availableGroups to recommendedGroups

We should be able to group by *any* key, this is just the recommended
list.
Find all keys from get_explore_data; use it for group pulldown

Here we create two arrays, one of our "recommended" list of group keys,
and one that we get from the get_explore_data API that returns all
the keys we have access to.

Using a checkbox, the user can have the pulldown show either the recommended
list or the entire list.
Merge branch 'concord-consortium-form-ui-tweaks'