v1.0.12 rc0

Release candidate for v1.0.12.

Includes a number of bug fixes, as well as new features, including:

• Undo/Redo support. Use either ctrl-z/ctrl-shift-z, or undo/redo from the Edit menu.
• Added a spectrum file export tool that allows more flexibly exporting spectrum files.
• Peak-skew support, with a handful of potential skew models. Right-click on a peak, and use the "Change Skew Type" sub-menu, or the "Peak Editor" to add fitting for skew to a peak.
• Ability to use .ECC files from ISOCS as detector response functions. Just drag and drop the .ECC file onto InterSpec to use.
• Ability to fit the functional FWHM equation from the current spectrum.
• A "FAQ" tab was added to the "Welcome" window, which answers many questions people have asked.
• Add reference photopeak lines for "Pu low burnup", "Pu high burnup", "Pu heat source", "U depleted", "U natural", "U 3% enriched", and "U 93.3% enriched"; to display these lines, type these names into the Nuclide field of the Reference Photopeak tab.
• Icons that can be clicked to create QR-codes and URIs has been added to various tools around the app; these QR-codes or URIs (of scheme 'interspec://') encode the state of the particular tool, so that the QR-code or URI can be used to get back to that same state.
• Not part of the release, but some short tutorial style videos are available at https://sandialabs.github.io/InterSpec/videos/index.html

No additional features are anticipated for the final v1.0.12 release, however, any bugs/issues found will be fixed, and small improvements to existing capabilities may be made.