Add more error messages and better error behavior
Added a bunch of new error messages that should show up in a terminal, inline GUI message (when available) or a dialog box. The latter is rare, but possible if a rectangle capture window is present with a screenshot failure.
The i18n UI strings need reviewing. Some of them are quite technical, but simplifying them wouldn't necessarily be better for the user or us. If there's an error, we need detailed info.
You won't be able to test much unless you're experiencing an error or deliberately modifying the code to trigger error messages. You can at least use SPECTACLE_IMAGE_PLATFORM=ImagePlatformNull spectacle -if to see the following UI.
Screenshot of new error message currently possible to see on X11 because of unrelated bugs:
Edited by Noah Davis