CP-9406: Make an unattended install of XenCenter

-Modified installer to support unattended install of XenCenter and prerequisite Microsoft .NET Framework 4.
-Normal behavior (no parameters used when running XenCenterSetup) has not been changed.
-All unattended install options will install Microsoft .NET Framework when necessary.
-Supported unattended install options for XC -- no user interaction is needed for all the followings:

1. install XC with default options (default folder, install for the current user only):
 XenCenterSetup /q

2. install XC to default directory, but install for ALL users:
XenCenterSetup /q /ComponentArgs "XenCenter":"ALLUSERS=1"

3. install XC to custom directory for the current user:
XenCenterSetup /q /ComponentArgs "XenCenter":"INSTALLDIR=""C:\Custom\Folder Where Spaces Are Allowed\XenCenter"""
(note the number of quotation marks, do not use  ALLUSERS=0)

4. install XC to custom dierctory for ALL users/per machine install:
XenCenterSetup /q /ComponentArgs "XenCenter":"INSTALLDIR=""C:\Custom\Folder Where Spaces Are Allowed\XenCenter"" ALLUSERS=1"
(note the number of quotation marks)

Signed-off-by: Gabor Apati-Nagy <gabor.apati-nagy@citrix.com>