Adding basic error handling to GUI

This PR adds handling of top-level uncaught exceptions to GUI, showing a dialog box with some context.
Debugging output to console is preserved.

For that purpose i almost completely wrapped all blight.rkt in blight-run function and added some context passing to error dialog (added to utils.rkt)

For now exceptions generated during blight-run() (the initialization) are *not* handled, because we need to split it to multiple sequential calls (like read-data(), connect(), init-gui(), bootsrap() etc).