Add functionality to copy Submodels from existing AAS files in menu

[zrgt]

• [x] Create template-folder where all template/example AAS files will be saved
• [x] The following should be implemented in PackTreeView class
• [x] Scan the template-folder with AAS files on opening AAS Manager: AASX Files
• [x] Scan the template-folder with AAS files on opening AAS Manager: JSON Files
• [x] Scan the template-folder with AAS files on opening AAS Manager: XML Files
• [x] Create for each AAS File in the folder a DictObjectStore-Object (like in the class Package) and save there objects which AAS File contains.
• [x] Create in a context menu of PackTreeview a menu "Copy and Paste existing submodel"
• [x] Menu "Add existing submodel" contains menus with aas file names from the template-folder.
• [x] Each of this AAS File menus should contain a list of Submodels in form of Actions
• [x] By clicking on one of this Submodels in the menu the following happens: the Submodel will be copied from the corresponding DictObjectStore and paste in current aas file. Before Paste a Dialog will be shown, where User can change attribute values of copied Submodel. (See anf if possible use here methods onCopy and onPaste in classes TreeView or in PackTreeView)