Introduce setter and getter for read only mode to application model
Toggle speed limit read only mode with action panel buttons
Set read only mode always after new layer is selected
Show editable speed limit selection field on edit mode
Add save and cancel buttons to speed limit form
Trigger application:readOnly event only if the state changes
Merge pull request #285 from finnishtransportagency/editable-speed-limit-form

Speed limit form edit mode