Rework backend + new elements about frontend

[Program132]

Goals

1. Easiest way to create your graphs, connect nodes (backend side)
2. Be able to set input as required or no (optional, by default it's true)
3. New class "Block" to create a "sub graph", a sub graph has a unique event node.
4. Engine detect and create "sub graph" without assistance (frontend)
5. Be able to have multiple events in one graph
6. Create other graphs (scripts) (frontend)

Concluded

1. ✅
2. ✅
3. ✅
4. ❌
5. ❌
6. ❌

[Program132]

Engine detect and create "sub graph" without assistance (frontend) ✅

[Program132]

Be able to have multiple events in one graph ✅

[Program132]

Create other graphs (scripts) (frontend) ✅