Reload All Images Button

[Avasam]

• The "Reload Start Image" button is now "Reload Images" and reloads every image: Splits, Resets and Start.
  • Images are no longer re-parsed when a run starts, which removes the small delay right after the timer starts. They reload automatically when you change folders, load a profile, or timer is reset.
  • ⚠️ This does mean your first split may be a frame or two longer ⚠️
  • Check FPS uses the images already loaded instead of re-reading them from the folder.
• Start and Reset images were not check for being valid images when validating the files in Split Image Folder
• A missing Start/Split hotkey no longer stops the other images from loading. The Start Image shows "not ready" and a warning. Auto-start starts working as soon as the hotkey is set, with no reload needed.
• If you load a profile with a missing or invalid folder, the previous profile's images are now cleared.
• The Start Image status no longer briefly shows "paused" after a run, since nothing actually waited at that point. The real Start Image pause, as described in the Tutorial, still runs after a match, with its countdown shown in the Split Image preview.
• Improved some wording in tutorial and error messages.

Extracted from #271, works towards #219