Installer rework - Audit.Log 

Issue #333 indicates that turning on or off Audit.log should be a mandatory choice when installing Service Control to production.  This is pretty sstraight forward for new installs but no so much ofr upgrades

The flag ForwardAuditMessages was changed from a bool to a nullable bool.  If the setting is not set  it is no longer assumed to be false

####  Fresh installs via the Adv installer Setup
For Platform Installer installs the chocolatey command passes an MSI switch "PlatformInstaller=true" this overrides the behaviour and defaults ForwardAuditMessages to off it is not already set in config.

#### Fresh installs using the Installer Setup

The GUI defaults to "not set" unless the existing config has a ForwardAuditMessages set to true or false.  Until a choice is made GUI doesn't allow install

#### Silent installs using the Installer Setup

This will now fail on fresh install or an upgrade if no existing ForwardAuditMessages exists 
```
Particular.ServiceControl.1.x.exe /quiet  
```
Needs to be this to succeed
```
Particular.ServiceControl.1.x.exe /quiet ForwardAuditMessages=true 
```

#### Command Line installs 
This kind of install happens when multiple instances are installed on the same PC  
When the 'install' command line switch is used the state of ForwardAuditMessages is checked and
if it isn't set already or on the command line as a option an error is throw prompting the user to add the setting as a command line option 
 
#### XCopy Upgrades
On start up the Service will log a Error indicating that ForwardAuditMessages should be set to something. in this case ForwardAuditMessages defaults to false.   
It's a nullable bool so would that mean no setting would equate to true