New methods for single PDF operations

[idircarlos]

It is necessary to create two methods called enableSingleOperationComponents() and disableSingleOperationComponents().
The goal of this method is to compact every enable or disable method of every single operation ir order to have less lines of code.
For example, now we have:

if len(selectedItems) == 0:
       ...
        disableCountElements()
        disableRemoveComponents()
        # later on we would have disableExtractComponents()
        # later on we would have disableSplitComponents()
       ...

We need:

if len(selectedItems) == 0:
       ...
       disableSingleOperationComponents()
       ...

Note: There is no disableMergeComponents() in the example because is a multi operation (multiple PDFs)