Add web:install command

It's currently possible to deploy a war file using the webbundle protocol. For instance, the following works fine:

karaf@root()> bundle:install -s webbundle:mvn:org.apache.karaf.examples/karaf-war-example-webapp/4.3.0-SNAPSHOT/war?Web-ContextPath=example

However, it's maybe not so straight forward for users. As we have web:list command, it makes sense to provide web:install and web:uninstall commands.