Deleted Patterns still exist in graph-view

[mbeisel]

Describe the bug
Deleted Patterns still exist in graph-view (branch https://github.com/PatternAtlas/pattern-atlas-ui/tree/fix/pattern-navigation )

To Reproduce
Steps to reproduce the behavior:

1. Create 2 new patterns

2. Create a Link between them via graphview

3. Delete one of the Patterns

4. (Reload page)

5. Pattern is deleted from the cards and from the related pattern section, but it still shows the pattern and the link in the graph view

6. Reformating graphview in frontend solves the problem -> frontend issue

Expected behavior
Either:

1. It shall not be allowed to delete Patterns with Links (bad option in my opinion)
   or better:
2. The Pattern and Link shall be deleted in the Patterngraph aswell