Add feature to expose server-side functions in shell

Add a shell helper command to read and make available the server-side functions defined in the "system.js" collection.

There are a few options:

1.) When you "use database-name" it would read all the functions from the server and define them in the javascript shell.
2.) Add a db.loadServerScripts() function to do 1
3.) Add helper method to the functions to expose them in the shell