Create dialog for filtering snapshots

[shilorigins]

The dialog will be launchable from the snapshot list view, and will contain the options for filtering which snapshots are displayed.

Alternate Design

Filters could be applied on each table column individually. We may look into this in the future, but the dialog option is simpler to implement and has fewer constraints on the filter options.

[tangkong]

Examples for filtering list view models exist already in the search page's FilterProxyModel, if you would like to use this as reference.

[tangkong]

Also, could we expand how this is different / expands on the functionality provided from #56 ?

[shilorigins]

I don't know that the functionality will be different, but this is part of an alternate search page layout.