Document and clean some stuff of DSLib

[Miepee]

This goes through IGMSerializable, GMWarning and GMLists and does the following changes:

• Use single file namespaces for them, and clean unused usings
• Document most of the attributes and methods and adds todos on what should still be documented
• Rename all occurences of Unserialize and rename it to Deserialize.
• Rename the GMSerializable interfaces to adhere to naming standard.