New logo design

Move the logo to a dedicated branch `corporate-design`. Automatically
deploy PDF/PNG/EPS versions of the logo to branch `logos`. Create a
pyMBE banner in two alternate versions for light and dark themes.

README.md

@@ -1,3 +1,9 @@
+<picture>
+  <source media="(prefers-color-scheme: dark)" srcset="https://github.com/pyMBE-dev/pyMBE/blob/logos/logo_banner_dark_mode.png">
+  <source media="(prefers-color-scheme: light)" srcset="https://github.com/pyMBE-dev/pyMBE/blob/logos/logo_banner.png">
+  <img alt="pyMBE logo" src="https://github.com/pyMBE-dev/pyMBE/blob/logos/logo_banner.png">
+</picture>
+
 # pyMBE: the Python-based Molecule Builder for ESPResSo 
 
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