Fix install and uninstall slots connected in the MainWindow

I cannot figure out how it works when built with mingw?
Add 32 and 64-bit installers for MSVC10

To enable the redistribution of npackd-gui binaries
Ask the user to create the installation path if it does not exists

I was bored about having to manually create it...
Also there is no apparent reason for not asking this.
Set the default installation directory to `QDir::rootPath() + "npackd"`

Setting npackd's default installation directory to %PROGRAMFILES% (what
WPMUtils::getProgramFilesDir() returns) is not a good thing because, on
64-bit systems, this would inevitably results in the installation of 32-bit
packages in the 64-bit directory. Per-example, Zip files of 32-bit packages
were installed in "C:\Program Files" instead of "C:\Program Files (x86)".

As the only alternative to the one I am commiting would be to have 2
different installation directories would not be coherent with any-CPU
packages, the default installation directory will be QDir::rootPath() +
"npackd" which equals to "C:\npackd" on normal Windows installations.
Support invalid certificate authorities by prompting the user

As having a valid certificate authority costs money and adding a custom
certificate in windows may be difficult for a newcomer.

The solution has been taken from:
http://support.microsoft.com/kb/182888/en-us

As labels and goto statements are present in both the msdn documentation
and the official npackd source code, I kept the one used in the knowledge
bulletin...
Fix the `unknown escape sequence \%` warning
Support local repositories and files

By simply adding an absolute (or relative to the npackd working directory)
file path with the file:/// prefix, users and packagers are now able to use
their own repositories and packages without having to host the files on a
web server.

Per example use the URL:
file://C:\Users\jdoe\directoy with spaces\my repository.xml
to reference the repository XML file located at:
C:\Users\jdoe\directoy with spaces\my repository.xml

This functionnality also offers npackd the possibility to have a full
offline support. Which means that npackd can rely on only local files
without requiring any internet access. Possibilities such as USB/CD
installers, personal packages and collections are now a little easier (some
little constraints are still presents).

Finally, even if would I still recommend to ban them from your file system,
spaces in file:// URLs are also supported.