Lots of refactoring again.

Changes:

• switched from .toml to .conf for keybinding configuration
  • it is more extensible because we can do key -> command rather than command -> key, allowing for dynamic commands
• use ncurses panels rather than windows for prompting user input
• refactor previous commands to make use of polymorphism/traits
  • I had this in mind already, just didn't know how to do it in Rust, haha
• switch from tree_magic in favour of mime_guess
• most common file operations are now working (might be unstable and cause index out of bounds though)
  • cut, copy, paste, delete, rename

TODOs

• fix crash when terminal is too small
• port over more commands from previous release
• better logic for displaying directory listings
  • particularly not forcing the cursor to be between index 0-offset
• add support for parsing ~/ and expanding inside keymap.conf for changing directories
• clean up code