Fix issue when selection is set without content

In some cases, you may have a selection set before the content it
loaded. If that happens things blow up. This checks to make sure we have
content before we try to operate on it.
Merge pull request #18 from CrowdStrike/selection-without-content

Fix issue when selection is set without content
Selections are now the actual content

Previously, selections were the Row items instead of the content of the
row.
Allow setting of selection before content is loaded
Clear selectionIndices if not found
Better row property handling

Use consistent naming and make sure that the properties are defined on
the ObjectController not the content itself.