Add Select-Plugins.ps1

Script to selectively enable or disable vCheck plugins via a simple GUI
Add plugin to select report header image

Simple plugin which must be run before any output-generating plugins to
insert user-selected report header into report.  Falls back to the
default Header.jpg if the file doesn't exist
Merge pull request #7 from philrandal/master

Add Select-Plugins.ps1 and plugin to select report header image