Draft: Add option for institute branded slides

Adds a branding option for placing institute logo and name on titlepage as well as substitute TUHH logo on content frames.

Also there are some formatting fixes included, as the TUHH wordmark had a white padding.

.gitlab/issue_templates/institute_logo.md

+### Institute Logo Document Class
+
+The following checklist should be used to add institute logos to the repository.  
+Please follow the checklist and use the provided template files to get correct spacings and sizes in the logos.
+
+Checklist:
+- [ ] Added titlepage logo version to be placed next to the TUHH wordmark (Path: `.theme_imgs/x0_logo_titlepage.pdf`)
+- [ ] Added content logo version to be placed in the top right corner of content slides (Path: `.theme_imgs/x0_logo_content.pdf`)
+- [ ] Added document class option and template configuration
+    ```
+    % Institute Name (x0)
+    \DeclareOption{x0}{%
+      \institutebranded{.theme_imgs/x0_logo_titlepage.pdf}{.theme_imgs/x0_logo_content.pdf}
+    }
+    ```
+- [ ] Checked correct document generation
+- [ ] Assign this merge request to the current maintainer