Add more controller for ruler

[toanvc]

Add more controller: drag button, switch cm <-> inch <-> mm

[shalzz]

Hey, I'm willing to work on this as part of hacktoberfest.
Use a spinner instead of a switch to let a user choose between the three states?

[toanvc]

Yeah, whatever you want 👯

[shalzz]

I sent you a pull request which implements the above feature. Check it out.