Moved populate_measurements code into generic _populate function

populate_measurements and new populate_parsers now call _populate
Moved most of contents of Project.main into generic main

Created additional function to populate the database.
Added core parser object that's going to run the parsing functions
Added ROOT_PARSERS variable to project settings template
Refactored measurement and parser objects

They share so much in common it was screaming base class, so now there
is a Runner class they both inherit from.
Fixed a couple of bad variable references Project._populate
Fixed another bad variable reference in Project
Set Project._populate to ignore missing template_name
Added empty parsers.py to app and project templates
Added populatedb command to commands directory.
Re-organised measurements and parsers templates