Add Yocto icon and mapping

[deribaucourt]

Hello,

Yocto is a widely used project in embedded Linux development. It's extension currently has more than 70k users.

The chosen logo comes from the official website which I re-dimensionned.

Since it is converted to a monochrome, I had the choice between white and blue from the original color pallet. I chose blue because it's more colorful and distinct.

Concerned file extensions are .bb, .bbappend and .bbclass. The Yocto project also uses .inc and .conf files, but they are also used for generic file types which already have an icon in seti-ui so I chose to not apply the Yocto icon them.

Here's a preview of the new yocto icon: