* Image.cs: Fixed problem with PixelEncoding.Unknown value
                      Fixed bug writing bits to buffer
* Ncgr.cs: Support write "Invalid size"
* Ncgr.cs, Nclr.cs, Nscr.cs: Adding missing data when creating a new file.

* NitroBlock.cs: No need of abstract "Name" field since it can be
  obtained with GetType.
Added UpdateSize to update the block size before writing (a class is
  mutable so it can be changed)

* Importer.cs: Clean code.

* Program.cs: Added test for Importer.
Clean & refactor code applying Extension Methods.