Job param

Added ability to provide XML config file with -Job parameter.

File contains a GlobalVariables path, and defines which plugins to use (as well as a path to plugins).

This will allow a single install of vCheck to service multiple reports. Also will allow unification across vCheck repos (i.e. one install of vCheck to run vCheck-vSphere, vCheck-Exchange, etc. - this needs to be tested)

Config Example
<vCheck>
   <globalVariables>GlobalVariables.ps1</globalVariables>
   <plugins path="plugins-vSphere">
      <plugin>00 Connection Plugin for vCenter.ps1</plugin>
      <plugin>03 Datastore Information.ps1</plugin> 
      <plugin>99 VeryLastPlugin Used to Disconnect.ps1</plugin>
   </plugins>
</vCheck>