Marked headers as C++ for editor.
Fixed source name to be an absolute path.
Some GUI code for the application.

A dialog class for choosing data and images for pixel selection
in a formula, and an extension of QComboBox to enable the user
to add a file name to the box's content.
Replaced edit boxes by spin boxes to ensure that numeric values are used.

Added some checking on start/step/stop parameters.
Aded a call to the new dialog for obtaining information from
user about which data to use for pixel extraction.
Main window is now a singleton class.

Also some refactoring to separate the wrapper of the open file
dialog into a method of its own.
Changes to the way that window data can be accessed.
Minor formatting changes.
Added code for access to pixel data from existing images.

Added an expression to the parser for selection of a layer
of a stacked image.
All of this needs some extended testing, but tests during development
all do what they should.
Updates to build script to use new code.
Updates to translations.
Added static method to ComplexArray to read image stacks.

Made relevant changes to other code that requests image
reads so that it uses the modified API.