Add support for abstract classes and operations

[Matthias Schoettle]

Currently, it is not possible in the UI to change the abstract attribute of Class or Operation. I.e., abstract is already in the metamodel, but never used.

I suggest the following ways to edit this in the UI:

• Class: Tap-and-hold presents a menu to toggle partial and abstract. An abstract class is identified by its name written in italic font.
• Operation: The tap-and-hold menu contains an abstract option that allows to toggle the abstract property. An abstract operation is identified by its name written in italic font.
• If an operation is changed to abstract, the class needs to be made abstract as well (if it is not yet). I.e., in one compound command for proper undo/redo.

[Matthias Schoettle]

In case MT4j does not support italic font, you might want to look into this extension: https://code.google.com/p/mt4jextensions/source/browse/#svn%2Ftrunk%2FMT4j%20Enhanced%20Font%20Handling

[Former user]

References #310: enable/disable abstract type of operations (controller+view)

→ <<cset f676b3017524>>

[Former user]

References #310: enable/disable abstract type of class (controller+view) and 'class abstract if one operation (at least) is abstract' constraint added

→ <<cset 2f451daa33f4>>

[Former user]

References #310: removed setItalic method in RamRectangleComponent because not used

→ <<cset 1f94729990f0>>

[Former user]

References #310: message view disabled if operation is abstract and/or partial + resolved formatter error

→ <<cset 771db0d1181c>>

[Former user]

References #310: bug un-abstract a class with abstract operations + formatter errors fixed + Javadocs added

→ <<cset 4ba6ef8884e2>>

[Former user]

References #310: removed setItalic from RamTextComponent and added the switch inside the operation handler

→ <<cset e4b75c5e799f>>