Add the ability to convert a certificate to text

Add the ability to convert a certificate to text

Adds a function that will convert a certificate to human readable text
format using the openssl print function. This is useful for debugging
and for displaying the full details of a certificate (including those
parts not supported by the Qt API).

Change-Id: I27238d05df37f8b15ad09f8e761b06344631a9ce
Merge-request: 2
Reviewed-by: Peter Hartmann <peter.hartmann@nokia.com>
Reviewed-on: http://codereview.qt.nokia.com/551
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>