Handle multiple initialize calls more gracefully

[ryx]

Describe the bug
Currently the second call to datalayer.initialize results in an error message being output. That is unnecessary and not very user-friendly.

To Reproduce
Call datalayer.initialize twice.

Expected behavior
Datalayer should have no issues with being (re-)initialized as often as necessary. The second call should behave exactly the same as the first call.

Additional context
This is especially useful for unit testing and other scenarios

[ryx]

I am seriously unsure about this one, even tough it's my own idea.

Related questions:

• How would we handle the initialized event for the second and following calls?
• How would we treat already added plugins or settings? Override? Extend?

[ryx]

Seems more like an enhancement or architectural change.