Update version to 1.0.47

Proper cleanup before exit when GLAD fails to initialize.

Playing around with GNUInstallDirs.

Slight code cleanup on paste. Same behaviour. Better comment for 16bpp.

Update deb copyright year.

Slight cleanup to horizontal pad of nav-bar at various UI sizes.

Contact sheet generator dialog now supports user-specified fill colou…

…r for empty pages. The colour-picker only shows up if the number of pages is bigger than the number of available images. The fill colour for contact sheets has a separate entry in the config since it has a different default (transparent black). Elsewhere (rotate, resize-canvas, etc) the fill defaults opaque black.

Increased version to 1.0.40. Fixed tacent version with a GIT_TAG. Upd…

…ated GIF save to use proper alpha threshold save-param variable.

Update tacent tag to fix Clang compile warning.

Fixed tacent git-tag version in prep for release.