OP_INSERT works

Any error will most likely be caused by the lego class for
OP_UPDATE which has not yet been debugged. Comment this block
out if necessary (will have no effect on the insert command.
Refactor legos using the Mongo_op class

The Mongo_op class has been added as a class inherits from sulley's
'block' class and is a parent of every lego used for communicating
with MongoDB. Its purpose is mainly two-fold: 1) remove code repition
accross previously created legos 2) create wrappers for lines seen
in multiple legos that may change - for example there is a wrapper
for pushing bson documents, which hopefully will become more complex
in the future.