Show loading icon during lazy load.

Change expand/collapse icon to loading icon during load.
Disable expand/collapse behavior during load.
Move expand/collapse icon HTML to factories.
Merge branch 'dev' of https://github.com/centerforopenscience/hgrid into feature/loading-icon

Conflicts:
	dist/hgrid-nodeps.min.js
	dist/hgrid.min.js
Merge branch 'feature/loading-icon' into dev