bootstrap virgin glastopf installations with dorks from mnemosyne 

This is the initial work for #30.
By default this feature is disabled, need a bit more live testing before i would recommend enabling it by default.

The following conditions must be met in order to execute the dork extraction from mnemosyne:

* pages dir is empty (vanilla installation)
* mnem_service is set to True in glastopf.cfg
* requests (python module) is installed.