- Add a new convenience feature to create slots.
When trying to connect some signal to a slot in the local class, always offer a "Create Slot" option to automatically create a slot that exactly matches the signals signature and the typed text in the editor within the local class.

When the item is executed, the slot is declared within the class, and is added to connect(..) call like a picked slot. (this is not perfect yet, but works ok)
- Fix several bugs in the code-completion
- Only show builtin types in type-completion mode, instead of also showing other keywords
- Allow completing types behind "const "
- Allow non-type completion behind "for(; a < |".
- Propose implementing non-class functions using the implementation-helpers