Fix for #719

Several changes in the way the Tables enumerate its fields.

- No longer flatten the source to display the table view.
- Use fromSources filter to dig into source hash structure to find
fields when displaying the view

- Trigger actual field loading on fields list opening
- Use current search result to update the field list when the list is already visible in view at search time
- Cache micropanel flattened data
- Tabular view flattens data when drawing