#20877: standalone environments have their shell lifetime scope disposed as well

Work Item: 20877
Adding disposable pattern to ShellContext
#20842: Fixing that a ContentPickerField looses its value(s) if an other editor group is updated

Work Item: 20842
Using ShellContext.Dispose() where applicable
Merge branch '1.8.x' of https://git01.codeplex.com/orchard into 1.8.x
Revert several projects.
Revert some more csprojs.
Revert another csproj.
Update two .cs files from 1.8.x.
Update the piece meal recipes.
Add piecemeal recipes. Add a ListingsSidebar shape template.