Feature/cameras/abstract lightfield camera

Description

Introduces a AbstractLightfieldCamera class.

This class provides methods, that all derived microlens-based lightfield cameras will need. In particular:

• A lightfield camera adapted constructor

• _calc_ideal_whiteimage to calculate a whiteimage from all available whiteimages which is used in th calibration process to find the microlens centers.

• _calc_microlens_centers to calculate the microlens centers from the ideal whiteimage.

Todos

• Tests
• Documentation