Nexpy

* Major improvements in reporting errors. In the shell, only one-line error summaries are output for readability, with full colorized tracebacks stored in the log files (opened with Ctrl+Shift+L). All uncaught GUI errors are displayed as full colorized tracebacks in a dialog box, as well as in the log files.
* Requires confirmation before exiting the program from the shell using `exit` or Ctrl+D.
* In the tree view, tooltips now display the short version of NeXus trees without attributes and with a recursion level of two to improve readability.
* Fixes compatibility with the latest version of `spec2nexus`.
* Adds support for `mplcursors` in Python 3.
* Improve information concerning external links in the GUI views of NeXus fields and groups.
* Prevents changing the class of NXlink objects in the GUI Rename Dialog.
* Restores the plotting window in the Fit Dialog if the user closed it prematurely.

* Fixes handling of errors with PyQt5 for versions later than 5.5, which trigger a program abort even when an exception is caught! Now, all uncaught exceptions produce a dialog window containing a full traceback. Such errors are also logged.
* Adds a `Restore Plugin` menu item to allow previously saved plugins to be reinstalled.
* Switches plugin imports to use `importlib` instead of the deprecated `imp` module.
* Fixes a bug with plotting data with unresolved links.
* Fixes a minor glitch when resizing of plot windows, caused by a change in Matplotlib v2.

* This fixes an incompatibility with Matplotlib v2, which prevents figures being exported to, e.g., PNG files.

* NeXpy is now compatible with PyQt4, PyQt5 and PySide.
* Note that, if using PyQt5 for the first time, plugins and importers that reference QtGui modules may need to be edited to change the imports to QtWidgets.
* Fixes a problem caused by a PySide bug that causes a segmentation fault on launch.
* If `h5pyd` is installed, a new "Open Remote File" menu item is available for referencing data stored remotely. This feature is under development.

- Fixes a bug preventing recent files from being correctly read on Windows
- Fixes a bug causing multiple rectangles to be plotted displaying the projection panel limits

- Enables copying of projection limits between projection panel tabs.
- Allows configuration of the projection panel rectangle color through the customize dialog, by making it the same as the grid color.
- Ensures that the projection panel rectangle is still visible after a replotting with different skew angle.
- Fixes bug preventing the 1D Customize Panel opening.
- Prevents invalid values of the aspect ratio being set.