Do not show the previous graph if a RRD graph cannot be downloaded from the server.
Have RRTool.Graphs only return devices with graph enabled just like RRDTool.CreateGraphs otherwise the client thinks there are more simple graphs than the server generates.
Also ignore rrd .png files.
Added a JSON rrdtool.generate method that calls RRDTool.GenerateGraph and return the .png name
Change FEditGraphs.ButtonGraphSave_Click to properly quote strings and pop up and error message if something is wrong.
Changed RRDTool.GenerateGraph to generate the .png name itself and return it.
Check the output of rrdtool graph for errors and if so log them
Make the Graph Editor preview also work for Client-Server and pop up an error window when appropriate.
Removed unused GetNewValueNum function
In case of error write more detailed information to the main log
Added support for Client-Server RRDTool.DeleteRRD using rrdtool.deleterrd
Merged RRDTool.DeleteAllRRDs with RRDTool.DeleteRRD
Merge pull request #8 from danfos/rrd-fixes

Fixed: RRD and other fixes.