Include new OEF logo in tutorials

[jh-RLI]

1. include in template tutorials
2. review current tutorials

[jh-RLI]

Since we used a URL (http://openenergy-platform.org/static/OEP_logo_2_no_text.svg) to include the logo in tutorials, a generic name should be used for the logo file (e.g. OEF_logo). This way we have a unique and persistent source for the logo file and don't have to touch the URL in the tutorials when changing the logo in the oep in the future.

[christian-rli]

@Ludee could you please provide permanent links to the new logos (or a link to a central location where those are described) here? Then we can link all new logos in one run.