Use our new logo in appropriate places

[daoudclarke]

Some places where we can use this:

• Search engine front-end
• Favicon
• Readme
• Wiki home page
• Open collective page
• Github page
• Extension icon

[ColinEspinas]

Just made some variants to help with the integration of this new logo.

I went ahead and used a white accent instead of letting the color transparent.
I'm open to propositions for updates.

I'll probably use this comment for future updates.

Fully filled with white accent:

This is destined to be used as an avatar to avoid weird cropping by platforms (e.g. the GitHub organization logo as a weird background when using the original one).
This also avoids the accent color to be transparent and the logo being unreadable on specific backgrounds.

Fully filled banner with white accent:

This is a banner for various usages, I recommend using it at the top of the readme file.

Rounded square with white accent:

This is the same as the one posted above but I filled the logo with white. Use this as a logo instead of the transparent one, this will prevent issues with backgrounds.