Add customizable keybinds

[TypicalAM]

Customizable keybinds would allow for rebinding any of the list/viewport/tab keys to for example have custom vim keybinds or using the command key in mac instead of ctrl.

[TypicalAM]

If someone would take a stab at this, things to consider are the following:

• Where can we save the keybinds (additional config file, something like the theme?)
• Do they, upon loading, override the DefaultKeymap package variables? or we introduce another structure to inject them
• What format do we save in (the bubbles.key.Binding needs a bit of work to be serialized)

[TypicalAM]

Solved by #59