MODE-1784 - Changed the way ModeShape web apps are deployed via the AS7 kit

Instead of statically packaging web applications into the kit and copying them over in the AS7 deployments folder, the following changes were made:

- the web applications were moved into a _deployments_ folder under the _org.modeshape_ AS7 module
- the AS7 subsystem was extended, with ```<webapp name="" exploded="" auto-deploy=""/>``` directly under the ```<subsystem>``` element
  - _name_ represents the name of the folder or file inside the _deployments_ folder
  - _exploded_ (default true) indicates if the packaged web app is exploded or not
  - _auto-deploy_ (default true) indicates if the web application should be deployed automatically, when the subsystem starts
- based on the above, web applications from the _deployments_ directory are deployed at runtime, when the subsystem starts