[WIP] Freeze feature:
* Define all flags
* Set/clear bit transactors
* Report trust line state
[FOLD/WIP] Enforcing
    * Enforce at source
    * Enforce intermediary nodes
    - Enforce in order book processing
    - Enforce global freeze (fix in pf!)
    * Don't consider frozen links a path out
    - Handle getBookPage
[FOLD] work in progress autobridging/freeze tests