Highlight arrows when source/target selected
Highlight arrows when source/target selected

Based on some of my suggestions in #21, I've made it so
that selecting a source or target table will highlight
the arrows originating/terminating at the box.

I've chosen some bold colors (bright magenta, lime green)
to show off the feature.  Feel free to change them if you'd
like.

OHDSI/WhiteRabbit,MaximMoinat/WhiteRabbit