feat(keybinds): improve default keybindings

[imsnif]

This changes some of the default keybindings to make them more intuitive. Namely:

1. All modes now have the quicknav ALT shortcuts (eg. ALT + n to open a new pane)
2. After performing actions that tend to be one-off actions, we're sent back to Normal mode (eg. opening a new tab, opening a new pane, closing a pane, closing a tab, toggling pane fullscreen)
3. Space no longer resets to normal mode, we are now left with ENTER and ESC. The upshot being that we can set tab and pane names with space in them :)

THIS IS A BREAKING CHANGE FOR THOSE WITH CUSTOM CONFIG FILES
In that we're changing the default config. Your custom config files will still be given priority, but given that we've changed the default, they might not do what you want them to. So, if you:

1. Have custom config files that don't change the keybindings - you're safe. This will not affect you.
2. Have custom config files that change the keybindings but you use unbind: true to unbind the default keybindings - you're safe. This will not affect you (but you might want to try the default keybindings again, we made cool improvements).
3. Have custom config files that change the keybindings but you don't use unbind: true at their top - you might want to make sure everything is okay. We're still going to give your custom files priority, but the defaults have changed. You might want to give things a go-over to make sure your changes still make sense for you.