chore: use new logo and add file association

[SethFalco]

Logo

Replaces the logo of the extension with the official Bats logo. I thought this was fitting, as it's now officially maintained as part of the Bats organization.

I made the following changes:

• Optimized the logo with SVGO and confirmed that there is no difference.
• Adding padding to the top and bottom and centered the content in that space so that the image was a square.

File Association Icon

Includes a file association icon which uses the Bats logo. So *.bats files will now have the Bats logo as the icon.

Typos

Read through some of the documents and fixed typos. I haven't rewritten any of it, but I may opt to do so in a separate PR, especially as the contribution guide is effectively defined twice.

[brokenpip3]

@jetmartin can we merge it?