Slurm plugin patch

A Client requested a plugin to do very specific server connexion using slurm. In order to achieve that it is necessary to open the server launcher and configuration interface. The modifications are as following :

1. Make some methods from pqServerConnectDialog virtual so they can be redefined in inherited class
2. Move all unnamed namespace declared class and methods from pqServerLauncher to pqServerConfiguration, and make these methods public so they can be used from a class handling pqServerConfiguration.
3. Mode pqServerFileChooser from Components to Core, so it can be used by the precedent methods.
4. Move the regexp command expand to command method so command method can generate an expended command if necessary.