Add functionality to remove old modules when machine is updated to a new profile

[viananth]

When user updates machine with a newer profile (eg. 'latest'), old modules must be removed.
"Update-AzureRmProfile -Profile 'Latest' [-Confirm] [-Force] [-RemovePreviousVersions]" will install latest modules and uninstall old modules.
-Confirm will ask user if it can download and install required modules.
-Force will override the confirmation
-RemovePreviousVersionswill uninstall old modules
Without -RemovePreviousVersions flag, the user will be prompted for confirmation of old modules removal.

[viananth]

This issue was moved to Azure#3300