Changed GetAddInName() when searching for Bitness of Office 14+ to account for 64bit OSs

Added logic to look at correct hive on 64bit machines for determining Office 2010+ Bitness.  Also ignore Office version if Bitness not found.

In GetAddInName() I was coming up with NULL for the RegistryKey [rkBitness], thus returning [string.Empty].  I found this was due to my 'SOFTWARE\Microsoft\Office\14.0\Outlook' key hiding in the Wow6432Node branch.  Determining the correct base key fixed this problem for me.

OS: Win 7 Ultimate (64bit)
Office: 2010 (32bit) - without Outlook installed.