add Connection Line Arrow

[dushibaiyu]

add Line Arrow and config

[nolankramer]

Thanks for this @dushibaiyu. Would you mind adding a picture to the PR description to show what this looks like during dragging and when connected?

[paceholder]

A picture would be really nice. Thanks

[dushibaiyu]

[nolankramer]

Thanks @dushibaiyu. So far it looks pretty good. Although two points for improvement:

• The default arrow-head color should match the default line color
• It looks like the arrow is not drawn at the head of the line while dragging - this should be fixed before merging