Support writing in tiled core

[danielballan]

This PR adds for writing data into Tiled from the client, like so:

tiled serve catalog --temp

from tiled.client import from_uri
c = from_uri("...")
c.write_array([1, 2, 3])

This is a large PR that has been about a year in the making, based external prototypes by @jmaruland and @kleinhenz and numerous discussions with @tacaswell and @dylanmcreynolds and helpful feedback from many others.

This code is "alpha" quality, and it has many known gaps that I will enumerate in GH Issues. Nonetheless, since Tiled is still in the "alpha" stage, I will merge it shortly and tag an another alpha release to get it more easily into the hands of our early users for feedback.