EZP-23128: As a developer, I want to be able to install PlatformUIBundle with composer without warning

JIRA: https://jira.ez.no/browse/EZP-23128

# Description

Adds the PlatformUIAssetsBundle as a dependency so that:

* it's not needed to run bower anymore (and node is now only needed for hacking/running the unit tests)
* composer post install scripts are happy to find the files :)

# Tests

manual tests