Ensure menu creation sequence is consistent.

[freakboy3742]

The existing app startup sequence is inconsistent between platforms, as it doesn't guarantee:

1. That system-installed app commands are installed before startup() is invoked
2. That the change listener is added to the command list after commands have been fully created
3. That menus are created after the initial menu state has been established.

Derived from #2244.

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct