Remove hardcode for PointModel in DefaultLinkWidget.tsx

[ToTheHit]

Checklist

• [x] The code has been run through pretty yarn run pretty
• [x] The tests pass on CircleCI
• [x] You have referenced the issue(s) or other PR(s) this fixes/relates-to
• [x] The PR Template has been filled out (see below)
• [x] Had a beer/coffee because you are awesome

What?

Remove hardcode for PointModel in DefaultLinkWidget.tsx (☞ﾟヮﾟ)☞ https://github.com/projectstorm/react-diagrams/issues/938

Why?

1. Hardcode is bad
2. In current version of DefaultLinkWidget users can't use custom Points

How?

Simply using the already existing LinkModel method ༼ つ ◕_◕ ༽つ

Feel good image:

[dylanvorster]

click noice

[dylanvorster]

ill try get this merged soon after some testing on my side as well