Support cross-layer requests in the query panel

[nmco]

It should be possible to filter features on a layer that have some geometric (INTERSECTS, DWITHIN, etc..) relation with another layer. For example, find all the schools that are close to floodable bands. It should also be possible to filter the features by attributes. For example, how many schools intersects floodable bands of type dangerousness 1.

The workflow to execute a cross-layer request in MapStore interface is as follow:

1. Select the main layer from the tree, enabling the query panel. Field the query panel as usual.
2. Click on the cross-layer request button (on the toolbar).
3. Two fieldsets will be add to the query panel and the query panel will become disabled.
4. Select the second layer, enabling the query panel.
5. Fill the second layer related fieldsets (geometry operation and attributes filters).
6. Query the data or produce a graph.

The chart reload options should take in account the cross layer fieldsets.

This module will require GeoServer cross-layer filtering extension.

Tasks:

• Do some tests with the GeoServer cross layer extension.
• Add the two extra fields sets to query panel.
• Change the filter production to includes the cross layer values.
• Add the cross layer button to the toolbar.
• Tie all the components together based on events.
• Extend charts state save and reload operations to include the cross-layer values.