Adds in toggleable crosshairs

[elistone]

Solves issue #5.
I did run into some issues with running the project which need up needing an extra module "babel-polyfill" because of ReferenceError: regeneratorRuntime is not defined babel/babel#5085

Though I saw you had "babel-plugin-transform-runtime" it still did not work for me.

[Irev-Dev]

Awesome, really happy with your work. I'm seeing a lot of white space changes which is my bad, I really should have set up a linter by this point.
I'm really happy that you have the crosshairs update as soon as the check boxes changes and not wait for another change on the canvases themselves for it to apply.
The polyfill issue is a little weird after I installed it and added the .babelrc file it started working without importing it into the project so 🤷‍♀️ It's probably best to have it explicitly imported as you've done.

I've got a commit that I'll push soon (on my phone can push now) where I've just added the cross hair colors and the transparent color into variables.

I'll merge this soon, but I'll likely put another issue up later to get the cross hairs to display on page load. Thanks for your help.

[Irev-Dev]

👏