This involves lots of changes:

- Andor cameras are instances of `andor_device_t` which extends `tao_camera_t`.
  This is similar to Phoenix cameras which are instances of `andor_device_t`
  which also extends `tao_camera_t`.

- The API for `tao_camera_t` had to be adapted.  The underlying principles are
  clarified in the documentation.

- Virtual methods for Phoenix camera have been updated accordingly.

- TAO core library provides more routines useful for servers.

- Phoenix server has been modified and simplified.

- Andor server has been rewritten and is much more similar to Phoenix server.

- Thanks to the (updated) unified camera API, controlling camera acquisition is
  more simpler and more consistent.  The code for the servers is also simpler.

The code compiles with no errors but bugs are expected.  A great deal of the
code for the Andor and Phoenix servers is identical.  This code should be
shared.