[Feature] Aspect Ratio, UI, README, more.

[Disonantemus]

Today I used 4 the 1st time cropgui, installed from AUR (Arch Linux), defaults to gtk and it's ok, also I did try the github version, and I found the following:

1. Overwrite image: maybe some Option or preference to not remove in another step when reviewing a lot of screenshots/images/photos.
2. I missed more aspect ratios like:
   • 1:1 4:3 16:9 16:10 21:9 and the same vertical ones.
   • I know you can use Shift to keep original AR.
3. README.md fixes:
   • It's not clear that you can install GTK version and defaults to TK, and maybe should default to GTK.
   • I didn't found how to remove cropgui when you installed from github following README.
   • Keyboard shortcuts don't appear.
4. Alternative Install:
   • If it's just python and some shell, it's possible to do pip install' or maybe using pypy3?
5. GUI:
   • It's weird that Quit' button it's on the open file dialog, you can have one last button to do that.
   • About/Help with info, like keyboard shortcuts (Like Shift) that are not shown at any place, and I just found because searching aspect ratio at Issues.
   • Next Image button: very useful when you are reviewing a folder to crop.

I like the fast way of cropgui and that it's the only jpg lossless native linux gui crop, that I know.
Hope you give this ideas a chance to improve user experience.

[howff]

I would also like to see the current filename in the window titlebar