hugin: updated to 2018.0.0

2018.0.0:
The version 2018.0 is mainly a bug fix release and introduce some minor new features.

Several improvements for optimizer tabs:
- mark deselected images
- allow changing optimizer variables for all selected images at once
- option to ignore line cp
hugin_stacker: New tool to stack overlapping images with several averaging modes (e.g. mean, median).
Hugin: Added option to disable auto-rotation of images in control point and mask editor.
Nona, verdandi and hugin_stacker can now write BigTIFF images (for files >4 GB). The output of BigTIFF has to manually activated on the command line. It is not set automatically. (For a complete panorama in BigTIFF you will probably also need enblend/enfuse from repository. The last released version of enblend does not yet support writing BigTIFF files.)
Added expression parser to GUI: This allows to manipulate several image variables at once. (This is the same as running pto_var --set from the command line.) This can be used e.g. to prealign the images in a given setup and then run cpfind --prealigned to search control points only in overlapping images.
Add user-defined assistant and expose it in the GUI. It allows to set up different assistant strategies without the need to recompiling. Provide also some examples (scanned images, multi-row panoramas with orphaned images, single-shot panorama cameras).

(adam)