* Close vulnerability and optimize digiline_send

`digiline_send` as it previously existed was vulnerable to a
time-of-check-to-time-of-use vulnerability in which a table could be
sent, size-checked, and then modified after the send but before
delivery. This would allow larger tables to be sent. It was also slow
because it called `minetest.serialize`. Fix both of these by
implementing custom message cleanup logic which simultaneously computes
the message’s cost.

* Clean up interaction with Digilines

Use `minetest.global_exists` to avoid an undefined global variable
warning when operating a Luacontroller with Digilines not available. Use
the new `digilines` table in preference to the old `digiline` table.

* Copy received messages

When a Digiline message is received at a Luacontroller, copy it so that
local modifications made by the Luacontroller code will not modify
copies of the table that are being passed to other nodes on the Digiline
network.

Register both luacontroller and microcontroller variations of detector craft recipes.

Fixes:
1. Lack of 'safe' on minetest.deserialize usage
2. String sandbox bypass via (""):evil()
3. Loss of upcoming digilines messages on server shutdown
4. LCs failing to show information on some errors
5. Interrupt IDs as infinite data storage

Fixed method name to get the position.