vtkGitFunctions module and Tester added. prep run : 2 tests failing.
All tests OK.

In vtkInitializeGit, one must redirect the output flow of "git init"
using the *relative* path.
Tests actually working.

- vtkGitFunctionsTester's Setup broke after the test of vtkGitInitialize
(error 75). Fixed it by updating the Teardown.
- corrected the vtkConfiguration sheet (Git functions was not set
  properly)
Code a bit cleant in the vtkGitFunctions module
vtkGitFunctionsTester module a bit cleant.

- names changed
- comments added
New module vtkFileSystemUtilities created from existing code.
New module vtkFileSystemUtilities.

in vtkFileSystemUtilities
- Deletion of the content of a folder
- Deletion of a folder
- Is a folder empty or not

in vtkFileSystemUtilitiesTester
- Tests for the above

in vtkConstants
- Added the global constant VTK_RETVAL_OK = 0
vtkCleanFolder only with Dir not working
vtkCleanFolder : back to FileSystemObject

vtkConstants
- added constant VTK_RETVAL_UNEXPECTED_ERROR = 2000

vtkFileSystemUtilities
- added function vtkCleanFolder_Dir that doesn't work
- vtkCleanFolder is now with FileSystemObject
In vtkGitFunctions : updated check of Git install
Updated vtkInitializeGit.

NB : prep run not yet working (tests not yet updated)

vtkInitializeGit :
- 2 optional arguments : textLogFolderName and textLogFolderPath
- Cleaner Shell calls
	- no "cd"
	- "/c" instead of "/k"
- addedFunction vtkGitConvertWinPath
Updated vtkFileSystemUtilities and vtkGitFunctions

- vtkFileSystemUtilities
	- improved functions, working with hidden files and folders

- vtkGitFunctions
	- return values updated
	- vtkInitializeGit : log file not yet implemented

- vtkConstants
	-  updated list of return values (to be moved ?)

- Tester modules uncommented as code is now transparent.

- Added third-party module ShellAndWait from cpearson
	- removes the need of waiting for one second when executing Shell
	  commands
Deleted isGitInstalled function.
vtkInitializeGit now only allows folders on C:

- not so good. But filtering is centralized in vtkConvertWinPath function
  in case we implement a workaround

- VTK constants are now Strings to avoid type mismatches during Tests
Updated vtkInitializeGit and error management.

In vtkGitFunctions
- vtkInitializeGit
	- updated log file management
	- updated error management

-vtkGitConvertWinPath
	- updated error management

In vtkGitFunctionsTester
- updated tests for new error management
Added a .gitignore in the project folder.

This file allows to commit with Excel running.
Removed vtkDeleteTreeFolder function.

Replaced all occurences in the code by vtkDeleteFolder
Added creation of .gitignore files in folder tree.

- In vtkFileSystemUtilities
	- added function vtkCreateTreeFolderWithGitIgnoreFiles
	- modified error management of vtkCreateTreeFolder

- In vtkMainFunctions
	- in vtkCreateProject, call vtkCreateTreeFoldeWithGitIgnoreFiles
	  instead  of vtkCreateTreeFolder

- In vtkCreateTreeFolderTester
	- added tests of vtkCreateTreeFolderWithGitIgnoreFiles
	- modified tests of vtkCreateTreeFolder so it fits with the new
	  error management.
Modified so a project has only one .gitignore
vtkGitInitialize updated with git add

All the files present in the initialized folder will be added to the git
repository.