Fixed timer behavior

If a z-axis slideshow was running when new data is plotted, the timer
was not stopped and future slideshows were frozen.
Further refinements to slideshow operations

A slight refactoring of the code
Updated merge-tiffs

This script is customized for a particular application at the Advanced
Photon Source, but can be used to guide the formation of similar
command-line scripts.
Added an in-place addition operator
Added the original filename to the NeXus output
Improved handling of quit requests

There was no proper call to close the QCoreApplication so secondary
windows would remain open after an attempting to quit.
Removed in-place addition

It works for adding the complete dataset but not for a slab, so it is
safer to remove it for now. Also removing set_changed from the _setdata
method. The value of an NXfield does not affect its representation on
the tree.
Added data value to the coordinate output

This appears in the options tab when the mouse is within a 2D plot.
Replaced "Replot" button with a toolbar action

This makes the button smaller, preventing some size issues with long
z-axis names. Also added tooltips for the whole toolbar.
Improved naming of imported data

Will now attempt to name the root after the imported file name, or, in
the case of multiple files, a common prefix or the directory name. It
uses the same algorithm as for opening NeXus files.
Added ability to handle reverse rotations

Can now define a starting rotation angle (omega), step size, and
whether it's increasing or decreasing.
Updated documentation
Updated to v0.1.4
merge master changes into this branch