Fix coding style
Enable on-line configuration changes

All properties can now be changed while the operation runs.
Fix handling of processor objects while paused

Changing the thread count always deleted the processor even when the
operation was just paused. Now the processor is recreated only if
needed. The current (sub-perfect) solution is to stop the operation
if the processor needs to be changed.
Fix coding style
Change semantics of parentOperation()

The function now returns 0 if the _direct_ parent is not a
PiiOperation. Previously, the closest PiiOperation parent was returned.
Change semantics of parentOperation()

The function now considers direct parents only and returns a
PiiOperationCompound*.
Hide PiiInputController interface

Moved the implementation to the Data class.