Replace File & Source Code release

After a lot of cleanup and ensuring proper licensing, the source code of GDImageDB is now available on https://github.com/SpiceOctopus/gdimagedb under MIT license. Have fun tinkering with my little hobby project :)

With this release, a small feature has been added: "Replace File".
Right click on an image and select "Replace File" to replace the file in the database with a new one while keeping all tag and collection affiliations of the original.

There have also been a lot of minor UI changes. The color scheme is more consistent across the entire application, new icons have been added, and most of the engine internal dialogs have been replaced with custom ones.