Port and refactor jackrabbit-webapp module to Oak

As mentioned at [1] we should port the jackrabbit-webapp [2] module to Oak and refactor it to run complete Oak stack. Purpose of this module would be to demonstrate

1. How to embed Oak in standalone web applications which are not based on OSGi
2. Configure various aspect of Oak via config

Proposed Appraoch

1. Copy jackrabbit-webapp to Oak repo under oak-webapp
2. Refactor the repository initialization logic to use Oak Pojosr to configure Repository [3]
3. Bonus configure Felix WebConsole to enable users to see what all OSGi services are exposed and what config options are supported

This would also enable us to document what all thirdparty dependencies are required for getting Oak to work in such environments

[1] http://mail-archives.apache.org/mod_mbox/jackrabbit-oak-dev/201508.mbox/%3CCAHCW-mkbpS6qSkgFe1h1anFcD-dYWFrcr9xBWx9dpKaxr91Q3Q%40mail.gmail.com%3E
[2] https://jackrabbit.apache.org/jcr/components/jackrabbit-web-application.html
[3] https://github.com/apache/jackrabbit-oak/tree/trunk/oak-pojosr