Make plugin more keyboard friendly

[shbach]

Already briefly mentioned here but creating an issue to further elaborate and for better tracking.

Right now the plugin isn't the most keyboard friendly. When the pop up is activated I have to then use my mouse to select the desired emoji. Ideally I can just type until I have a match then press enter without having to leave the keyboard. This means the first result in the list has to be selected, arrows can be used to navigate, and enter/tab could be used to insert.

I think looking at the way others do it such as Discourse and Github could be a good reference.