Fixing analysis errors
Fixing errors described in Code Analyzer.
Added null checks.
Fixed string comparison errors.
Added default ENUM values
Moving some constants into centralized Constants.cs cleaning up strings and ensuring null checks.
A few more string comparisons to fix
Made lock object readonly in logging utility.
Removed a Where and made it simply a FirstOrDefault.
Merge branch 'master' of https://github.com/OfficeDev/PnP.git