Part 1 of refactoring of Get-DecryptedObject

[andreasjordan]

Get-DecryptedObject needs two things:

• A Dedicated Admin Connection (DAC) to select master.sys.syslnklgns
• A WinRM connection to read "HKLM:\SOFTWARE\Microsoft\Microsoft SQL Server$serviceInstanceId\Security"

That's why Get-DecryptedObject needs $Credential which it used all the time, but the parameter was missing.

I also added documentation and restructured the code for better readability.

The command has still the code to open a DAC itself, which will be removed as the last step after all the commands that call this command are also refactored.