2 file formats: old simple and new zipped

This commit makes Pencil able to read and write in 2 file formats:
1. old simple - file format used by Pencil "all the time" - PCL file + DATA directory,
2. new zipped file format - single PCLX file

When you choose "Save as..." from File Menu - you write filename,
and then if filename extension is PCL - Pencil saves your work in old Pencil file format,
when you choose another extension - Pencil saves your work in new zipped file format - in a single file

When you open a file - Pencil checks this file if is zipped or no (here Pencil pay no attention at file extension),
and if file is zipped - Pencil tries to open it as a PCLX file,
and if file is not zipped - Pencil tries to open it as a regular PCL file.

This commit has been checked only on Linux,
I tried to compile it on Windows but it was for me unsuccessful.

In order to use zip functionality I have used QuaZip library.