The CheckableComboBox editor (= multiple choice combobox) is too restrictive

[vld-codra]

This issue is linked to issue #21 which should be resolved first.

This issue results from the rollback of Depends on selection in the Task Tree from a CheckableComboBox editor back to a QLineEdit.

The CheckableComboBox editor attached to DTypes.MULTIPLE_CHOICE is not flexible enough to fit all needs. In some instances, it may be handier to directly modify the QLineEdit at its top rather than clicking mutliple times. It cannot display keys nor indexes during selection which can make selection tidious when there is a lot of choice. The current item also cannot be set easily as its selection may depend on the underlying data type...

Possible work leads:

• Derive CheckableComboBox classes to implement the variations. This solution may require to also implement variations of MULTIPLE_CHOICE datatypes
• Create new DataItem attribute(s) and CheckableComboBox options to handle this variation as is already the case since v2.0 with the DefaultChoiceMode enum.