Adding new way of calling data2plot in subclasses

[mateczentye]

In calculate_data method of the superclass will initialise and populate a dictionary full with the data grids as values and data2plot strings as keys. All the variables will be moved into individual try/except blocks as it turns out some dimensions can be missing.. This should allow flexibility for 1, 2 and 3D vector quantities.

• move all variables into own try blocks
• add all the initialised variables to the global data dictionary
• finish up all the energy/power term integrations
• make unit test to check if values been added dict by looking for the keys - also test the exceptions