Also fixed add tool function, it was swapping the last tool in the toolbar group, instead of adding it.

Hi! Huge thanks for the PR!
Can you remind me of what issue is this fixing?

I didn't see the issues created but I've found the bugs when experimenting with adding and removing tools.

This PR should fix two issues:

• removeTool function, it's using 'slice' for removing the tool, from the array of tools ( an array of keys) of a toolbar group, but the result of 'slice' is not being used, in turn the tool doesn't get deleted. I changed it to splice as splice actually modifies the array without having to reassign to itself.

• addTool function: when adding a tool and not giving the function an index, instead of adding the key to the array of tools of a toolbar group, the code is just overwriting the last tool key.