Change EmsFolder#hidden? to allow for overrides.

https://bugzilla.redhat.com/show_bug.cgi?id=1086015
Add Hash#sort! and Hash#sort_by! core extensions.

https://bugzilla.redhat.com/show_bug.cgi?id=1086015
Split out x_build_single_node from x_build_node.

https://bugzilla.redhat.com/show_bug.cgi?id=1086015
Bypass tree walking code with an upfront query for the vandt tree.

https://bugzilla.redhat.com/show_bug.cgi?id=1086015

This change improves performance via a pipeline of methods that
- Query the entire vandt tree using the Relationship model.
- Prune the tree as much as possible for unused parts
- Prune via RBAC and remove empty folders
- Sort the tree
- Preload records for what's left
- Convert the relationship tree to a UI tree structure for dynatree.

The spec against a real database has gone from 23.1s to 4.3s, which is
an 81% improvement.  Cumulative performance including ee267dc9, the spec
has gone from 33.2s to 4.3s, which is an 87% overall improvement.

Note that the performance is also consistent regardless of the depth of
the folder structure of the tree.
Added a check to add parent nodes only on trees other than vandt tree.

Added a check to add parent nodes based on @sb[:open_nodes] only when active tree is not vandt tree. VandT tree no longer needs to add parent nodes when clicking on a VM as we are building full tree on initial load so all parent nodes already exist in the tree.

https://bugzilla.redhat.com/show_bug.cgi?id=1086015
Merge pull request #131 from Fryguy/fix_ui_vm_summary_3

Fix UI vm summary performance (part 3)