**************************************************************************** Button Routines.

FileExists checks if a file exists and is not a directory.

MustBox returns a new gtk.Box, with the given configuration, if err panics.

MustButtonImageStyle returns a new gtk.Button with the given label, image and clicked callback, if error panics.

**************************************************************************** DialogBox Routines.

MustCSSProviderFromFile returns a new gtk.CssProvider for a given css file, if error panics.

MustGrid returns a new gtk.Grid, if error panics.

MustImageFromFile returns a new gtk.Image based on the given file, if error panics.

MustLabel returns a new gtk.Label, if err panics.

MustLabelWithCssClass returns a stylized new gtk.Label, if err panics.

MustLabelWithCssClass returns a stylized new gtk.Label, if err panics.

MustLabelWithImage returns a new LabelWithImage based on a gtk.Box containing a gtk.Label with a gtk.Image, the image is scaled at LabelImageSize.

MustOverlay returns a new gtk.Overlay, if error panics.

MustProgressBar returns a new gtk.ProgressBar, if err panics.

MustWindow returns a new gtk.Window, if error panics.

TODO: Clean up StrEllipsis(), StrEllipsisLen(), and TruncateString() and consolidate into a single function.

Required environment variables.

Required environment variables.

Optional (but good to have) environment variables.

Optional (but good to have) environment variables.

Optional (but good to have) environment variables.

Optional (but good to have) environment variables.

Optional (but good to have) environment variables.

Required environment variables.

LabelImageSize default width and height of the image for a LabelWithImage.

OctoScreenVersion is set during compilation.

LabelWithImage represents a gtk.Label with a image to the right.