Set min/max Gif speed

Is your feature request related to a problem? Please describe.

Many current gifs on the web and created through various programs set gif frame speed to respect the minimum speed most browsers go by. This means that the large majority of gifs downloaded and played with ImageGlass play too fast - and the currently IG-approved "re-encode the gif" makes working with gifs in IG far too tedious and frustrating, especially given that most image-viewers play them at reasonable speeds without issues.

Describe the solution you'd like

The ability to change the min/max speed at which ImageGlass plays gifs would completely eliminate the issue, and make ImageGlass one of the better gif viewers out there as well

Describe alternatives you've considered

Using a different image viewer. Who wants to spend multiple minutes each time they wish to view a gif to re-encode it, just so ImageGlass can play it back at a reasonable speed? I'm aware the problem lies with those who put the gifs together, but a solution is well with ImageGlass' reach

The issue names no files, tests, or entry points. Start by locating ImageGlass's GIF playback and frame-delay handling, then determine where configurable minimum and maximum playback speeds belong; done means GIFs respect those bounds and the settings can be changed by users.