Query Specs

Some technical specs for the query functionality.

Current issues

We have three plugins for querying: WMSGetFeatureInfo, MapQuery and WFSGetFeature. This is confusing. For example both the WMSGetFeatureInfo and MapQuery plugins are based on WMS GetFearueInfo, so which one to use?
These plugins override or overwrite private functions of OpenLayers. This may cause maintenance issue in the future. (Given our needs I'm not sure we can do much about that actually.)
Using the WMSGetFeatureInfo and MapQuery plugins implies creating an Ext.Observable object at the application level. Documenting this is tricky. It can also lead to maintenance issue if we need more functionality in this observable in the future.
Today c2cgeoportal applications define pieces/blocks of viewer. Again this is confusing, and difficult to document and maintain. Instead applications should define the entire viewer. This implies that creating a viewer should be as easy and straightforward as possible.

Clearly document in the API docs what functionality each plugin provides and what to use when.
Discourage using the MapQuery plugin. Can it be removed entirely? What are the applications that actually use it?
Write a plugin that plays the role of the observable. This plugin will be observable, as it will extend gxp.plugins.Tool, which itself extends Ext.util.Observable. The id of this plugin will be passed to query plugins.