The device list in the UI thread is replicated so we can show UI clients
the list without the need for a lock.
The previous implementation relied on loading and reloading of the device
list from the store every time an event changed either the devices or their
trust state.
This leads to a couple of ineficiencies leading to timeouts while
waiting on the database lock if a user has a large number of devices.
The new implementation never loads devices in the UI thread from the
database, they get passed through the thread queue by the main thread
which already holds them in memory.
