Adding support for logging using vtkLogger in ParaView.

* command line options (-v) enable users to specify log verbosity for
  messages shown on stderr by default.
* command line options (-l) allow users to request multiple log files with
  different verbosities.
* vtkPVLogger implements a category-based logging framework that allows
  users to elevate log levels for predefined categories at runtime using
  environment variables.
* proxies support a logname attribute that gets set with user
  friendly name to make it easier to interpret log messages.