Issue 205: Reset drag states when dropping, even on invalid targets

[cbroeren]

Closes #205 : Dropping a dragged object into invalid target breaks the component sidebar

Description

After dropping any element on an invalid target, the component sidebar was staying disabled.

In this PR

• Making sure that the drag state is being reset, even after dropping on an invalid target
• Add a generic resetDrag function so we can trigger that from different places, and for future improvements keep the logic of resetting the state in one place

Before, it was just returning from the drop even handler when the target was invalid, but the draggedObject was still set. Therefore the app still thinks it's in drag mode, and disabling the component sidebar.

Testing Notes

1. Open any of the page editors
2. Use the sidebar to drag a component (any will work)
3. Drop the component on the most outer wrapper (the fake browser content)
4. Verify: The drag mode is reset and the component sidebar can be used again

Before / After

Before	After
Stays in drag mode, component sidebar disabled	Resets drag mode, interaction enabled

[leandrocp]

🎉