Support project specific artifacts feeds

[richardgavel]

The various artifacts related Cmdlets should support an optional -ProjectName property to support project specific feeds

Add-VSTeamFeed
Get-VSTeamFeed
Remove-VSTeamFeed
Show-VSTeamFeed

Get-VSTeamPackage
Get-VSTeamPackageVersion
...

[SebastianSchuetze]

I checked for "Show" cmdlet it works by default without the project flag. No need to add one. But for the rest I will implement it.

[SebastianSchuetze]

@richardgavel just finished the main work and I will merge it soon and publish it probably directly today.