* Removed direct usage of `transport` object in device drivers.

   There are currently only 3 methods that still use the transport:

    - `slave.srs.sr830.SR830.trace()`
    - `slave.srs.sr830.SR830.snap()`
    - `slave.srs.sr850.MarkList.active()`

   Closes #146.

 * The `slave.lakeshore.ls340.Curve.delete()`method now raises a
   `RuntimeError` when called on a read-only curve.
 * The `slave.lakeshore.ls340.LS340._factory_defaults()` method
   does not take the `confirm` argument anymore.
Updated Changes
Renamed `slave.core.InstrumentBase.transport` to
`slave.core.InstrumentBase._transport`, closes #147.
Updated CHANGES