Attach plugin panels to map inner div.

This will prevent users from dragging plugin panels above the header and
sidebar. It also simplifies some of the positioning logic.
Add ConstrainedMoveable widget.

This widget will keep plugin panels and the map legend within the bounds
of the map during drag and resize operations.
Merge pull request #217 from kdeloach/topic/panel-clipping

Ensure plugins are visible after window resize and split screen events.
Make layer_selector node IDs deterministic.

Using a static int to generate uniqueIDs for nodes is problematic
when nodes load in a different order. To make node IDs deterministic
we derive them from the text value and their position in the tree.
Replace deprecated event in feature compare plugin.

The ArcGIS API 'update' event was deprecated in v2.0 and replaced with
'update-start' and 'update-end'. Features seem to load more consistently
using the 'update-end' event.
Merge pull request #219 from kdeloach/topic/share-save-fix

Fix some issues with save/share