Replace deprecated Oxygen-Sans font with Noto Sans

What does this MR do?

KDE changed default font from Oxygen to 'Noto Sans' quite a while ago (2015, I guess). So "Oxygen" is kind of abandoned/deprecated font in 2019. However GitLab still forces it. Which makes GitLab far less readable compare to other websites. So I placed "Noto Sans" instead of "Oxygen".

Screenshot

FullHD monitor, Kubuntu 18.04 with KDE.

Left (Oxygen-sans, OLD) | Right (Noto sans, NEW)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team