Improve the scripting environment

[jkarder]

Some improvements can be made:

• If an INamedItem is stored in the VariableStore, the name of the item can automatically become the name of the variable.
• Renaming variables should be possible by pressing F2.
• Removing variables should be faster.
• Selecting multiple variables in the VariableStoreView should be possible.
• Scrolling inside the code editor should be possible when compiling and executing scripts.