Fix local/velocity X/Y spaces and add side booleans to add_velocity

[Alluysl]

• Fix the bug where using the X and Y axes of local and velocity spaces in add_velocity would lead to undefined behavior
• Add client and server fields to both actions, true by default; if set false, the action will be cancelled when executed on a player on that side
• local_horizontal is now unnormalized, the old one is now named local_horizontal_normalized
• Clean up the code (switch moved from EntityActions to Space)

Tested all edge cases I could remember of, and more generic cases as well (the times are slightly underestimated):

The transformVectorToBase method is made public for access in the bi-entity action. It doesn't feel very encapsulated but - in my opinion - it's not worth creating a toGlobal static method that accepts two entities just for this purpose.

Optimized code by the way :P

@eggohito I have a documentation page draft, if and when this is merged, DM me

[apace100]

Looks fine for me. :) Will merge this into the next feature update (not patch) since it adds serialization data.