* invalid models can be highlighted on stash
* selection mode can be toggled between single/multi selection (where applicable)
* color for highlighting can be set
* finetuning of menus
* add functions to apply changes to selected objects
* allow to highlight models by their model strings
* Utility function to show which parts come from DB
* model strings can be obtained sorted/unsorted
* will allow to highlight entities
* nested custom menus
* moved displayAutomatically() menus in view base class
* fixed which menus are displayed for aircraft models
* also changed to QStandardItem model to see if this is causing any trouble (the real bigger changes will follow in #530)
* for new value objects (e.g. distributor, ...)
* new modes are required (e.g. CStatusMessageListModel::Simplified)
* model filter allowing to filter models
