Added a listener for vector features

There are new two vector loading listeners: one that returns the notification with the feature data and another that simply provides the notification.
Altered to prevent unnecessary callbacks

If we don't have the appropriate listener, then we don't need the callback to be invoked.
Added a listener behavior for view changes.

This listener will be invoked whenever the map view is changed (zoomed or panned).
Added files missing from last commit.
Added a listener that provides feature in extent data.

Similar to the listener that provides the current view extent except it also provides all of the feature data in the extent.
Merge branch 'master' of https://github.com/wicketstuff/core
Added a new page to demo WFS functionality.

I also fixed a bug in the feature click handler where clicks on features that lack an "id" property result in hiding the popover.
More work on the demo page.

Resolved issue with logging messages.
Merged in a couple more files.
Increased the size of form content.

This is a Jetty setting to increase the amount of form data we can post
back from the example application.
Worked on clustering.

I also did some code cleanup.
Fixed typo in the ignore file
Added links from examples to Java code
Added click handler to clustering example
Added Travis CI profile
Updated Travis CI profile
Fixed a couple minor issues.
Optimized imports for the project
Added demo link to the README
Merge branch 'master' of https://github.com/wicketstuff/core