mgr/dashboard: Reload all CephFS directories

mgr/dashboard: Reload all CephFS directories

Now angular tree is used instead of ng2-tree, as it provides a better
way to dynamically load children and it provides a way to update all
children without losing all track of everything.

The loading icon will rotate now on any fetch.

The tree will detect new directories and removed directories.

It's also now possible to select the root directory of a CephFS in order
to create snapshots of the whole FS.

Fixes: https://tracker.ceph.com/issues/42617
Signed-off-by: Stephan Müller <smueller@suse.com>