Fix problems when adding ConfigSections

[craigfowler]

When adding <configSections /> elements to the application configuration file, we must only ever add them at the beginning of the file. We cannot add them partway through.

This is a problem for ZPT-Sharp right now.

The current best solution is in this StackOverflow answer. It needs to be applied to all of the NuGet package transforms which create the configSections element.