Work item state commands

[jhoneill]

PR Summary

New commands to manage the states available to a WorkItem type in a custom process. (In the default processes the WorkItem types are fixed). States are things like "New" "Done" etc. and the user can hide the built-in states, unhide them, and add or remove custom states. So there 5 new commands Get-VSTeamWorkItemState gets a list of the states for a given WorkItem type Add-VSTeamWorkItemState adds a custom type to the list Remove-VSTeamWorkItemState removes a custom type the was previously added Hide-VSTeamWorkItemState hides a system type from the list Show-VSTeamWorkItemState unhides a system type which was previously hidden

Each command has its own help file and unit test, and there is a format XML file to display the states as a table.

PR Checklist

• [X] Write Help
• [X] Write Unit Test
• [X] Update CHANGELOG.md

[DarqueWarrior]

Does this PR also have changes from 338? Some of these look familiar.