Enh depthpane refactor

modified depthline view to be more robust, to handle locked and overwrites, and handle current_surface_from_bin line (not edit mostly). Changed edit logic to update non data traits immediately but handle data via buttons. 
implement zoom toolbar icons
cleaned up several files
also added self-save method to survey line 'save_to_disk'.  This just needs a survey io function to call to save itself to disk, with appropriate hdf5 methods.  It also needs to have the project_dir set when it's created in line with the hdf5 rework branch.