EEwsConnection: Rename 'password_lock' to 'property_lock'.
EEwsConnection: Remove the EProxy.

EProxy is deprecated.  Will replace with the new proxy API.
EEwsConnection: Add a "proxy-resolver" property.

This property is bound to the internal SoupSession's "proxy-resolver".

The EEwsConnection's "proxy-resolver" property can then be bound to
the "proxy-resolver" property of one of the EDS base backend classes.
EEwsConnection: Integrate GProxyResolver in backends.