Support for snippets that contain flows

The goal of this release was improve support for snippets that themselves contain flows so that implementing more complex components such as galleries or form builders is easier. To that end:

• The FlowMgr class now supports a syncFlows method making it possible to resync with the page after a snippet is added or deleted.
• After a snippet is added or deleted the we force a resync with the page to pick up any new or removed flows.
• I've also added in support for setting a label against flows (rather than just the Id) so that nice human friendly labels can be set.