Move schedule downlink tab to first position

[kschiffer]

Summary

Closes #7188

Changes

• Move the position of the Schedule downlink tab to the first position and select it by default

Testing

Steps

• Go to the "Messaging" tab of an end device

Results

• Observe the Schedule downlink tab being selected and in the first position
• Also, Dowlink and Uplink tab captions have been changed to Schedule downlink and Simulate uplink

Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Compatibility: The changes are backwards compatible with existing API, storage, configuration and CLI, according to the compatibility commitments in README.md for the chosen target branch.
• Documentation: Relevant documentation is added or updated.
• Testing: The steps/process to test this feature are clearly explained including testing for regressions.
• Infrastructure: If infrastructural changes (e.g., new RPC, configuration) are needed, a separate issue is created in the infrastructural repositories.
• Changelog: Significant features, behavior changes, deprecations and fixes are added to CHANGELOG.md.
• Commits: Commit messages follow guidelines in CONTRIBUTING.md, there are no fixup commits left.