Added test mode in editor and puzzle download

[Sense101]

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This PR adds a test mode in the puzzle editor where you can test the puzzle you are making and restore the solution when you turn off the test mode.

This also adds an import and export button underneath the title where you can download and upload puzzles as .bin files.

It's a few very simple changes which should greatly improve the experience of creating puzzles.

And yes I know how to use scss now (I think)

Hopefully there are no bugs :)

[Sense101]

So in a nutshell, this PR can be split into the following changes:

• Added a test mode for the puzzle editor
• Added the ability to download puzzles for testing purposes
• Increased the gap between the two buttons while playing a puzzle

[tobspr]

Will take a bit of time to review :D

[Sense101]

This is now up to date with 1.4.3 code and potentially ready to be merged.

[Sense101]

Please note, the code is by no means final, just an overall structure of the addition proposed. I'm sure there are shorter ways of doing the same things, especially with the css.