Checkvist extended commands

Adds some more VIM oriented commands to Checkvist

# What It adds four new commands to Checkvist (https://checkvist.com) Commands: l - Expand node (same as `→`) L - Focus the list item (same as `Shift →`) h - Collapse node (same as `←`) H - Un-focus the list item (same as `Shift ←`) o - Add below (same as `enter`) O - Add above (same as `alt+enter`) G - Go to the last item in the tree (same as `End` or `Fn+Down`) alt+g alt+g - Go to the first item in the tree (same as `Home` or `Fn+Up`) meta+j - macOS users: Move list items down (same as `⌘ ↓`) meta+k - macOS users: Move list items up (same as `⌘ ↑`) You can find the code at https://github.com/NicoSantangelo/checkvist-extended-commands