Batch update cmdlets

[jasper-schneider]

New cmdlets for updating data in the Batch service.
Includes tests and help.

[azurecla]

Hi @jasper-schneider, I'm your friendly neighborhood Azure Pull Request Bot (You can call me AZPRBOT). Thanks for your contribution!

It looks like you're working at Microsoft (jaschnei). If you're full-time, we DON'T require a contribution license agreement.

If you are a vendor, or work for Microsoft Open Technologies, DO please sign the electronic contribution license agreement. It will take 2 minutes and there's no faxing! https://cla.azure.com.

TTYL, AZPRBOT;