Resolve "Memory Leakage: if setPlots get called multiple times, TreeModels get allocated and the pointer gets overwritten"

Description

Moved the initialization of the aspect model in the docks to the base class.

This solve the problem with the memory leak when multiple of objects of the same type are selected and set in the dock widget creating every time a new model that is never deleted.

Conformity

• Changelog entry
• Downport
• Unittests

Closes #776 (closed)