'location' and 'layer' targets for dataviews/panels

[dbauszus-glx]

A location dataview can be added to the location.view by specifying 'location' as the target. It should also be possible to add a layer dataview to the layer.view dataview panel. However, instead of specfying 'layer' as the dataview target it might be easier to use the layer panel / location view which nests the dataview object as the default target if not explicit to a target defined by a string value.

[dbauszus-glx]

The idea here is that testing will be much easier when i can have any dataview type, like json which doesn't require any plugin to be loaded on a layer view which doesn't require a database connection or locations to test display, reload behavior. For example for testing toolbars.