* Remove some unused variables
* remove duplicate "using .." by sorting and deduping the list
* Remove things that already exist in the parent class (in one case I moved some documentation to the parent)
* EntityBodyData and and NextSearch were never set (only read), removed
* _timeout was never read, subsequently _timer became unused. part of a TODO timeout functionality that was not implemented yet
**Changes**
Fixed a faulty change in logic that occurred during the Christmas GPL nightmare.
I stepped through Emby 3.5.2 and stumbled over a difference in the query between Jellyfin and Emby, where in Emby, query.ParentId was set to the item itself. So I did a little digging in the old GPLv2 source and found this https://github.com/MediaBrowser/Emby/blob/3.4.1.8/MediaBrowser.Controller/Entities/Folder.cs#L720
**Issues**
Fixes#673
Add Argument*Exceptions now use proper nameof operators.
Added exception messages to quite a few Argument*Exceptions.
Fixed rethorwing to be proper syntax.
Added a ton of null checkes. (This is only a start, there are about 500 places that need proper null handling)
Added some TODOs to log certain exceptions.
Fix sln again.
Fixed all AssemblyInfo's and added proper copyright (where I could find them)
We live in *current year*.
Fixed the use of braces.
Fixed a ton of properties, and made a fair amount of functions static that should be and can be static.
Made more Methods that should be static static.
You can now use static to find bad functions!
Removed unused variable. And added one more proper XML comment.
