Add an easy to access/obvious button to hide history panel

[ahmedhamidawan]

This is not something high priority, or something we have to do, but just a pet-peeve of mine that hiding the history is not very obvious? So, this is very optional and I can close this if we disagree.

Before	After

Note that the existing way to hide the panel still works!

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.

[mvdbeek]

This is great, I love it! This will also work on touch devices, where screen space is especially limited.