Add layer/group order to share-map params

[mulfvik]

It would be nice if layer and group order in legend together with map zindex being saved in share-map

[MattiasSp]

Some things to take into account:

• The solution should be opt-in so that the current behaviour is kept.
• May be best to focus on the "storeMethod": "saveStateToServer" mode, as the URL could become quite unwieldy.
• It would be good to not include the layer order if the user hasn't changed the default order.
• It would be preferrable if the configuration is made as general as possible to extend to all types of user states.
• A future extension could create a checkbox user interface letting the user choose what types of user states to include in the URL/mapstate.