SONARFXCOP-40 Run FxCop using the "/ignoregeneratedcode" switch

Added support for ignoring generated code in FxCop. As described on jira.

These changes need to be applied together with the changes on the fx-cop plugin (I also created a pull request for these changes) [SonarCommunity/sonar-fxcop-library#6](https://github.com/SonarCommunity/sonar-fxcop-library/pull/6)