1.3.0 - Image gallery

This version adds an image gallery (closes #3 (closed)) and moves getFileIcon to an external file (closes #2 (closed)). It also has error messages incase an external file fails to load.

The image viewer uses Bootstrap modals to display images with a consistent width and height (so the buttons won't be flying around the screen). It also implements listeners for the left and right arrow keys for easy navigation. It will only display images and will skip over non-image files.

This release also fixes some long-standing issues with exiting dark mode without refreshing.