Add read-only mode

[agarciadom]

To allow for modification of the model (whether it is to be stored on disposal or not), getting any many-valued feature returns a "proxy list", whose operations are delegated to the underlying EList in MagicDraw.

If the model is only to be read and never modified, it may improve performance to return the lists directly, rather than the proxy lists. This would dramatically reduce the number of roundtrips needed, for example, to loop over the list.

This would most likely need:

• An addition of isReadOnly() / setReadOnly(boolean) methods to the MagicDrawModel class.
• Extending the MagicDrawPropertySetter to throw an IllegalStateException if it is used when the model is in read-only mode.
• The extension of the ValueEncoder class in mdplugin.remote with a method to encode ELists of various element types.
• The extension of the MagicDrawPropertyGetter in two ways, if and only if the model is in read-only mode (existing behaviour outside of read-only mode should be preserved):
  • It will decode the returned lists back into an EolSequence.
  • It will refuse to decode a PROXYLIST Value and instead throw an exception explaining the issue.