ARTEMIS-4244 Set web config using system properties

[brusdev]

It is possible to use system properties to add or update web configuration items.
If you define a system property starting with "webconfig." it will be parsed at the startup
to update the web configuration.

To enable the client authentication for an existing binding with the name artemis,
set the system property webconfig.bindings.artemis.clientAuth to true, i.e.

java -Dwebconfig.bindings.artemis.clientAuth=true

To add a new binding or app set the new binding or app attributes using their new names, i.e.

java -Dwebconfig.bindings.my-binding.uri=http://localhost:8162
java -Dwebconfig.bindings.my-binding.apps.my-app.uri=my-app
java -Dwebconfig.bindings.my-binding.apps.my-app.war=my-app.war

To update a binding without a name use its uri and to update an app without a name use its url , i.e.

<web path="web">
  <binding uri="http://localhost:8161">
    <app url="activemq-branding" war="activemq-branding.war"/>
...

java -Dwebconfig.bindings."http://localhost:8161".clientAuth=true

java -Dwebconfig.bindings."http://localhost:8161".apps."activemq-branding".war=my-branding.war

[brusdev]

I added the support for binding and apps without names and a section in the Embedded Web Server doc.