SDK should use new CKE4 logo and branding colors

Two issues after branding:

The color of links in SDK is the same as in docs but it doesn't look great with the shade of blue that we have for CKEditor 4:

screen shot 2018-03-12 at 13 55 41

The samples (SDK) are sort of a part of the documentation (in CKE5 they are included in the Umberto-generated docs, CKE4 just uses a different engine and a separate page), yet it is not branded in the same way as the docs and samples for other projects.

CKEditor 4 docs: screen shot 2018-03-12 at 14 01 29

CKEditor 5 samples: screen shot 2018-03-12 at 14 03 02

Maybe we should use the "documentation" branding for the SDK as well to make it more consistent?

ckeditor / ckeditor4-sdk