Revert to old indent engine

[dgrunwald]

The MateY indent engine (introduced with #305) is too aggressive. Our old engine would 'learn' the indentation for a given scope when indentation only a portion of the document, so it usually inserted the intended amount of indentation when typing a newline. The MateY engine does not have this feature, which leads to user frustration whenever the indent engine's opinion on the correct indentation differs from the user's.

Also, the engine has major bugs when using the Allman coding style, causing the indent engine and the new code formatter (#306) to fight each other. When this happens, SharpDevelop is almost unusable.

We should revert to the old C# indent engine from SharpDevelop 4.x.