Added Customizable Shortcut Hotkeys

[Metacor]

fixes #38 - Configurable Hotkeys (with Modifiers - None/Ctrl/Shift/Alt) fixes #31 - only Shortcuts with an Active Hotkey have .preventDefault() - All Hotkeys can be disabled

Much of this commit can likely be truncated with the use of loops, but I couldn't figure it out.

• F-Keys: aren't being properly tagged with .preventDefault(), but they are still working as Hotkeys F5 is unusable and F1 is annoying - But I doubt many people are going to Hotkey F-Keys
• app.js @ 2142: I hard coded the toast position for Shortcut's 'Save and Reload' (fix this?)
• shortcuts.html: The blue color is from the README Logo, I used vars so it can easily be changed I also swapped the default 'Photo Editor' and 'Print' Hotkeys [CTRL + M <--> CTRL + P]
• about.html: I centered the main text and added a line break @ 'With Betterviewer...'

I didn't included it in this commit, but is the 'Help' folder actually needed? It seems to be an outdated copy of 'Pages', I deleted it from my private repo and everything seems to still work as intended.

screenshots: Previous Design | New Design

[Ademking]

Unique work @Metacor 🤯 You're a legend!!! Thank you so much for your time and effort. You made my day. ❤️