E2: Add entity:linkComponent(entity) function

[CaptainPRICE]

A function similar to what Starfall and Expression Advanced have.
To allow linking wire components (keyboard, cam/pod controller, eyepod, etc.) to the vehicle/prop (appropriately, to whatever entity a link demands to be linked to in order to make a successful link), make certain wiring stuff a whole lot easier.

A full usecase E2 sample, (by default) allowing only owner to type into the keyboard via seat:
https://gist.github.com/CaptainPRICE/0f0d445e437c1499f6a2ae2c8e95c1dd

Removing a link should be possible by passing noentity() as an argument (to avoid creating extra E2 function). Due to how linking works with some components, there will have to be a separate function for unlinking :/
Additionally, there should also be a function which could be used to return an array of entities to which a component is currently being linked to: array=entity:linkedTo().
These new functions should be a part of the wiring E2 core (which is disabled by default).

[CaptainPRICE]

See discussion at Discord (dev-wiremod).

[thegrb93]

I don't like reading discord. what's the problem

[CaptainPRICE]

(in short, just drama with gohidas/@adosikas.. Divran came and approved this idea as long as it is going to be a part of disabled-by-default E2 core, and wiring core is exactly that, as I proposed above)
So, reopening it, PR incoming.