File uploads handled by container / using filesystem namespaces

This is the first part of this work, main updates are as below:

* Rewrite of the inline (bolt/files/files) upload form to use the same container configured handler as the content file fields.
* Cleanup of a few Async commands to make sure they use filesystem namespaces.
* Implemented file duplicate functionality
* Some bug fixes to the file delete functionality
* Minor fix to Filesystem breadcrumb UI (there were cases where it was not being displayed)
* Some refactoring of the Upload handler to make it a bit more usable in multiple places.