Set default terminal to alacritty

[stevenhuyn]

Is useful when using the file explorer and right click contexts of open terminal here Also will update Ctrl + Alt + T behaviour.

I had to run sudo update-alternatives --config x-terminal-emulator to update the default terminal.

[Kasui92]

We already have hotkeys for alacritty, so I'm not sure overwriting the default here is necessary. And I've found that it's actually nice to have a way to use the system terminal in case there are any issues with alacritty.

From #129

[dhh]

I would actually reconsider #129 if we could make it work with the "Open in Terminal" from the Gnome finder. But the patch there doesn't do that. It only changes Ctrl + Alt + T.