Add image conversion module.

This module is optimized for importing photos (but can be used for
normal color scans too). It is able to apply a 3d-transformation
if neccessary; The rest of SDAPS can only handle 2d-transformation
so it makes sense to do this during the import step.
Add "custom" style.

This new style can be used to swap the internal functions that
retrieve information about images. Note that this style does not
support drawing any barcodes or similar by itself. You have to
ensure that you do everything yourself!
Add custom style to LaTeX style.
Split conversion into separate function.
Split addition of images into separate function.
Make csvdata functions callable externally.
Do not explicitly turn on draft mode.

Doing this means that draft mode can be disabled manually. This
may be useful in some cases, but is also a bit dangerous.
Make annotate API more useable.
Try to create an annotated PDF if there was an error during setup.
Allow different nesting depths for QObjects.