Bug 42489: Add a logger for the Lox module.

Bug 42489: Change "loxid" to "loxId".

This follows the camel case convention.

Bug 42489: Require a loxId argument for most methods.

This ensures that a method only works on the credentials of the
*expected* loxId, rather than the newest `TorSettings.bridges.lox_id`
value which may change during a session.

We also add `#activeLoxId` to stay in sync with
`TorSettings.brigdes.lox_id`. We merge `clearInvites` into its updater.

Bug 42489: Make loading the stored preferences unconditional on
the #credentials value.

Also change the type of `#events` to always be an Array.

Bug 42489: Generated loxId is unlikely to clash with existing ones, but
we add some free logic to guarantee this.

Bug 42489: Return copies of Lox module internals to ensure they cannot
be edited by a caller.

Bug 42489: Add notifications to the Lox module.

We ensure changes to credentials pass through #changeCredentials to
check whether we should send a notification.

Bug 42489: Add #assertInitialized.

Bug 42489: Change LoxError.

Move the LoxErrors types into LoxError. Only set the type if it is
specific.

Bug 42489: Change the Lox Authority URL.

Bug 42489: Try and re fetch the pubKey, encTable and constants if they
failed before.

For example, if they fail via a domain front request, we should try
again with `fetch` when we are bootstrapped.

Bug 42489: Make sure trust level strings are converted to integers.

Bug 42489: Tidy #attemptUpgrade by returning early with a promise.

fixup! Bug 31286: Implementation of bridge, proxy, and firewall settings in about:preferences#connection

Bug 42489: Listen for notifications from Lox module, and pass in loxId
to methods.

Bug 42489: Listen for notifications from Lox module.

Also, do not save the bridge_strings to the preferences if they come
from the Lox module.

In DomainFrontedRequests distinguish between reachability errors,
response errors and other errors in DomainFrontedRequest to improve Lox
error messaging.

Bug 42489: Drop getLocalizedStringForError from TorLauncherUtil.

Bug 42489: Drop nserror strings.