Closes #2306 - extend Admin-UI by permissions READTASKS and EDITTASKS

[SebastianRoseneck]

Sonarcloud: https://sonarcloud.io/summary/new_code?id=SebastianRoseneck_taskana&branch=TSK-2306

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Release Notes:

For the submitter:

• I updated the documentation and will supply links to the specific files
• I did not update the documentation
• I included a link to the SonarCloud branch analysis
• After integration of the PR, I added a description of changes on the current release notes
• I did not update the current release notes
• I put the ticket in review
• After integration of the pull request, I verified our bluemix test environment is not broken

Verified by the reviewer:

• Commit message format → (Closes) #: Your commit message. i.e. Closes Commit Hooks won't work without JIRA Tickets #2271: Your commit message.
• Submitter's update to documentation is sufficient
• SonarCloud analysis meets our standards
• Update of the current release notes reflects changes
• PR fulfills the ticket
• Edge cases and unwanted side effects are tested
• Readability