Fix back-button browsing and state after mutation events

[radiovisual]

Closes issues #20, #21. Adds new dependencies.

[sindresorhus]

I can't get it to work:

• Go to https://github.com/sindresorhus/hide-files-on-github
• Click Show dotfiles
• Click the index.js file.
• Click the browser back button.
• Click the Hide dotfiles button.
• Nothing happens

[radiovisual]

Whoops! I see what is happening. It seems that calling trigger() from within the injector is not working. The only thing that is working in my latest tests is to re-attach the click handlers to the toggle button upon each injection from within the injector's callback. For whatever reason the injector doesn't want to access the parent scope. I will run some more tests tomorrow and get this fixed.

[radiovisual]

Ok, you can try it now. The only way I can get it working after back-button browsing is to continuously attach the click handler. So you will see multiple calls to addToggleBtnEvents(). If a single call to this function is removed, the button will lose it's click event.

[sindresorhus]

Now the button doesn't work on the initial load.

[radiovisual]

Hm, that is weird. What is necessary to fix the initial load problem you are mentioning (which just got fixed in the latest push) is not necessary in the options branch I have going for the Options Page. There are a few mysterious forces at work here!

[sindresorhus]

I still can't get the button to work on load, but it works in the other PR, so merging. Thank you :)