Ildipo/celloptions

This adds a number of improvements to beaker:
* code cells have names and tags - a new dialog is used to edit these
* from JavaScript it is possible to start evaluation of named cells, tagged cells
* on the fly code can be evaluated from JavaScript 
* JavaScript cells can (SHOULD) return a deferred object if they are executing "event driven" code
* new language plugin loading mechanism
* notebook is now rendered before language plugins are loaded
* progress report for all operations (load and evaluate)
* JavaScript beaker.showProgressReport() function for partial cell output display

This addresses the issues #934 #933 #932 #916