Display error messages from Assembly.scad to user #33
Description
If Assembly reports an error when asked for a preview, display the error instead of the preview.
Example errors: invalid inputs, incompatible options.
The communication channel would be the output log, with lines like:
Echo: ERRORMSG: [Knuckle width must be at least 55]
Echo: ERRORMSG: [This design does not have a Gauntlet.]
Echo: ERRORMSG: [Hand is too wide. Width must be at least 67 for length 84.], ERRORLINK: [wide.html]
The message would be displayed in place of the preview, and the link would be presented, if provided, for the user to get more information (in a new window).