Support for FeatureInfo (Identify tool)

[andreasneumann]

It would be good if there could be feature info support (Identify tool) in the JS-QGIS API.

QGIS has different identify-tools modes:

• Current layer
• Top-Down, Stop at first
• Top-down (and return results for all layers)
• Interactive layer choice

For the web mapping context I think that the middle two versions (Top-Down, Stop at first; Top-down) would make most sense.

It would be great if this could support the QGIS expression engine and HTML for the display of feature info. See the "Display" section in the Layer properties:

That way we can be really flexible, with the mixture of HTML and QGIS expression support.