Create a powershell module

[zippy1981]

Acceptance criteria:

• Plaster created powershell module in new folder
• Publish to powershell gallery
• Move Invoke-EncryptColumns.ps1 and New-EncryptionKeys.ps1 there
• Move scripts to handle EF migrations there.
• Document all the cmdlets
• Move all powershell in the appveyor/ folder that isn't absolutely appveyor specific there.