Remove features and add Plugin capabilities to the Workbench Application

Currently, the i2b2 Workbench Applications users can add "features" to the workbench. The problem is two-fold; (1) Eclipse has stopped supporting the "feature" component of their RCP (Rich Client Platform). More importantly is the second problem in that users do not have an easy way to add a plugin to an existing workbench application.

Returning to building the workbench using plugins will allow users to have control over what plugins they can add to their workbench. Users will simply drop a jar file into their local workbench folders and the plugin will be available for use when they log into the workbench.