Silicon production from normal and desert sand

Ability to produce silicon either from "normal" sand or from desert sand.

Allow using any node in group:sapling for making glue

Moretree and Ethereal mods add a lot of saplings

Remove legacy code that enabled / disabled mesecon wires that were placed 2 blocks below a
pressure plate. From now on, please place a vertical wire at that place. That way, no false
signals will be triggered (the wire won't "flash" turned off if you enable it by a pressure
plate and turn off a switch connected to it).
If you depend on this functionality, please just revert this commit. That should be possible in
the near future as well, since no major rewrites are planned for mesecons_pressureplates. In the
long run, please update your mesecon strucutres to use vertical wires instead of relying on this
old hack.

Fix bugs in the Luacontroller (when placing, false input pin values were given) and fix variables
leaking into the global environment in pistons.

I hope this doesn't break anyone's setup.

However, without the print_count limiting functionality

Conflicts:
	mesecons_luacontroller/init.lua

Merge branch 'improve-luacontroller' of https://github.com/ShadowNinja/minetest-mod-mesecons into ShadowNinja-improve-luacontroller

Conflicts:
	mesecons/legacy.lua
	mesecons_luacontroller/init.lua
	mesecons_microcontroller/init.lua

Use minetest.override_item to redefine mese

Settings can now be retrieved by mesecon.setting(<name>, <default>) and can be modified without
editing the source code by adding the setting to minetest.conf
For instance, you can add mesecon.blinky_plant_interval = 0.5 to minetest.conf in order to
increase the blinking speed.
Rewrite the blinky plant with nodetimers.
Fixes #161

switch

circuits.
This also fixes a crash introduced with the previous commit that occured when placing a wire
crossing.

flexibility and because it was never inteded to be OOP in the first
place.

mesecon.receptor_on and mesecon.receptor_off are provided by wrappers
(mesecon:receptor_on/off) for compatibility, but will be removed. Mod
programmers that use mesecons: Please update!

Also, fix microcontroller polluting the global namespace and remove some
deprecated stuff.

This may also bring some performance benefit.

wires 2 nodes below them, allows to hide circuitry powered by them.
Fixes #179
Rewrite pressure plates + vertical wires using mesecon.register_node.

large machines.

It also makes the wires.lua code easier to understand and more
maintainable. In case any other mod depends on
mesecon:update_autoconnect, please update it to use
mesecon.update_autoconnect. This should also fix some other minor bugs.
Please report bugs if this commit creates new ones.

This commit changes wire looks and removes some unneccesary textures.

In case this fix creates new bugs, please report them.

Just some minor issues like dead code.

Changes:
  * Stops code after a certain number of instructions.
  * Allows functions, due to instruction counting.
  * Allows loops and goto with non-JIT Lua (LuaJIT doesn't count looping as an instruction, allowing infinite loops), due to instruction counting.
  * Removes string matching functions as they can be slow.
  * Adds some safe functions.
  * Limits the amount of printing that can be done (to prevent console flooding).
  * Code cleanup.
  * More...

using two ABMs allows the engine to desynchronize them, which makes the
duty cycle unpredictable.

Fix the commandblock's check for quiting the formspec