Create Test for Sequential Import of Transactional Data.

[nnikolopoulos]

Cases to be examined:

• Reimport of Opening where the Opening for CSM has been deleted and one for LC (same DataNode) added.
• Import Actual for GRIC [previous period] → Import Opening for GIC [current period] → Import Cashflow for GRIC [current period].
• Import Cashflow for GRIC [previous period] → Import Opening for GIC [current period] → Import Cashflow for GRIC [current period].

This issue is a residue of #140.

[nnikolopoulos]

A potential notebook where the cases above could be tested is: /Test/ImportStorageTest where check methods have already been implemented for similar cases.