Avoid a thread-lock when a configuration file is removed

A thread lock occurred due to recursive calls to
_ConfigurationDirectory.delete() when a configuration removal was
detected.
Added tests for ConfigAdmin with FileInstall
RemoteShell server thread named according to binding port
Poll time is now a property of the FileInstall component
Ignore conf/ directory
Renamed folderwatcher to fileinstall

pelix.services.folderwatcher -> pelix.services.fileinstall

The new name is more logical according to component names and comments