Add support for remote Windows Update installation

[LordHepipud]

In general it should be possible to install Windows Updates from the Icinga Web 2 module, in case the following requirements apply:

• The PowerShell Module is running with sufficient permissions to install updates
• The PowerShell Module has the command for installing updates enabled (disabled by default)
• The Icinga Web 2 users inherits the permission to install updates

If one of the above requirements is not fulfilled, this feature is disabled within the Web Module