Avoid IDs as JSON object keys in move format

[domob1812]

This changes the move format (mainly for character updates, but also some godmode commands and building updates) so that it does not rely at all on "IDs as strings used to index JSON objects". This change makes the format simpler and more expressive, especially with respect to the order in which updates are done. It also allows to update one character multiple times (in a defined order) within a single move. In addition to that, this also implements a new "waypoint extension" move, which appends a list of waypoints onto the already existing waypoints of some character.

Both changes together allow to implement proper and efficient convoy movement (sharing the main part of a long path between many characters) with the "principal directions" movement system.

This also includes a port of the first three commits from #170 to master from the 0.3 branch.

[domob1812]

For building update moves (for now, just setting the service fee), the new format is this (replacing a JSON object keyed by IDs with a single object or array of objects that have the ID explicitly as a field):

{"b": {"id": 42, "sf": 50}}
{"b": [{"id": 1, "sf": 50}, {"id": 2, "sf": 10}]}

Similarly, the format for character updates is also changed (except that the id for them can also be a JSON array of IDs for batched updates):

{"c": [{"id": 42, ...}, {"id": [10, 20], ...}, ...]}
{"c": {"id": 1, ...}}

[domob1812]

God-mode sethp and teleport are also changed from keyed-by-ID objects to arrays of individual updates that have an explicit ID:

{"god": {"teleport": [{"id": 42, "pos": {"x": 1, "y": 2}}, ...]}}
{"god": {"sethp": {"c": [{"id": 42, "a": 5, ...}, ...], "b": [...]}}}

[domob1812]

For the new waypoint extension feature, a character update can include a wpx field. It has the same encoded format (from findpath) as wp, but will add waypoints onto an already active movement (and is only valid if there is actually an active movement):

{"c": {"id": 1, "wpx": "..."}}

The main intention of this feature is to support movement of many characters as a convoy. For this, a common "initial waypoint" S must be chosen. Then each of the characters is sent to S, and all of them (with a batched ID list) have their paths extended from S to the final target T:

{
  "c":
    [
      {"id": 1, "wp": "from position 1 to S"},
      {"id": 2, "wp": "from position 2 to S"},
      {"id": 3, "wp": "from position 3 to S"},
      {"id": [1, 2, 3], "wpx": "long path from S to T"}
    ]
}

An example for how to do such convoy movement is in the integration test.