This PR updates the logos and branding guideline of Slint to match the new website design. The new logos are a 1:1 replacement of the old logos except for the circular logo. In the new logo design, there isn't a separate circular logo, as the square logo with circular crop can be used. Further, the logo folder also contains logos in CMYK for use in printed materials. The PMS is just the color value in the naming and can be used where Pantome colors are required. The README has been updated to explain which logos to use when as well as the Slint "blue" color.
* Give it a name that matches the svg it was created from
* Update gallery example to use the same logo
* Create a smylink to the old name in vscode-extension as that needs the
icon to be in that directory.
Examples will be able to use the logo from their location in `../../../logo/xxx.svg`
Some other things that needs to have the logo in their directory can use symlinks.
But because of the situation of windows, we can't use symlink for things our users
need to build and this is the case for the compiler-internal (because the C++ build
use the code from the repository), so there is a copy of the 'full' logo in
internal/comoiler/widgets/common
