Adds User functions + other improvements

[exchange12rocks]

1. Adds functions to work with User definitions.
2. Unifies code for User and Group parts for some functions.
3. Splits deserialization into several functions.
4. Improves docs for Group functions.
5. Set-GPPSection: Corrects an issue where adding new GPP objects into a GPO was not possible if the GPO has never had that GPP section before
6. Get-GPPSectionFilePath: Adds a feature to return a folder path along with the file path. To accomodate new Set-GPPSection's functionality