upgrade to Ext JS 4.2 and Sencha CMD v3.1.0.256

- added separate .gitignore to websocket-javaee7-extjs/src/main/webapp folder to exclude Sencha CMD's build directories.
- fixed Clear.data.ChangeObject class - removed explicitly specified base class Ext.Base (prevented Sencha CMD from successful app build)
fix .gitignore issue

Maven ignore rule "target" in the root dir was hiding Ext JS files
exclude "ext" and "packages" dirs from git tracking