Protractor cleanup for demo shell

[DenysVuika]

Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (check one with "x")

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation
• Other... Please describe:

What is the current behaviour? (You can also link to an open issue here)

What is the new behaviour?

• Cleanup all "synthetic" tests in protractor, i.e. those addressing the demo shell implementation rather than real-life scenarios
• cleanup dead code
• remove custom fonts from the demo shell
• remove various Viewer customisations in demo shell
• remove site picker from document list demo (not used)
• cleanup various css styles in demo shell

Does this PR introduce a breaking change? (check one with "x")

• Yes
• No

If this PR contains a breaking change, please describe the impact and migration path for existing applications: ...

Other information:

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

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