Implement creation of separate source files for each partial class definition

[monoman]

pattern: classname-suffix.cs expect for the original source containing the first members partial

Where suffix could possibly be:

• 'partialnnn' where nnn is a self-incremented counter (padded with zeros on the left)
• 'identifier' where identifier is the name of the first member in the file or have some UX to let the user fill in the identifier

[monoman]

Partially solved with RC1 - via Move partial to new source file