Bugfix: Apply tool panel filtering in workflow editor.
Bug originally reported by Eric here - http://dev.list.galaxyproject.org/Bug-Toolbox-filters-not-applied-in-workflows-td4662879.html (though this only fixes the superficial bug of them showing up in the workflow editor - and does not yet implement "strong" toolbox filters as requested).

This is actually a broader change that centralizes logic for listing out tool panel contents when displaying components to the user and the added filtering comes about from that. It also eliminates the last places Galaxy was accessing toolbox.tool_panel directly (in those mako templates).