steam-http: implemented a sending queue

The old message sending queue in SteamApi has been removed in favor of
handling queued sending within SteamHttp. This is more extensible for
working with other API calls that need to be sent in order with other
API calls.  Additionally, it prevents from having two queues to iter
through.
steam: reauthenticate after the account password is changed

After a Steam account's password is changed, all API requests return an
HTTP 401 (unauthorized) error. This is due to the fact that the API
access token no longer valid.

This issue is resolved by adding a set evaluator for the password set.
This will allows the plugin to know when the user's password has been
changed. Upon the password being changed, the current API access token
is discarded, the account is reconnect, and then the reauthentication
process beings.
steam: treat the token set as a password

The API token is "sensitive" information as anyone with the token can
obtain access to the API session. To better protect to token, it should
be treated as a password.
steam-api: use GLib format macro for guin32