Allow admins (i.e. players with the `protection_bypass` privilege) digging any command block

The handles were never used anyway

Reduce actionqueue complexity, thus faster execution
Improve code style
Add documentation/explanations

mesecons.tablecopy didn’t support recursive tables, while Minetest table.copy works well for them.

Recompress losslessly using `optipng` and `advpng`

This reverts commit d8f82e67.

Add check nil var with bug from crash server.
fixes #438

Saves on bandwidth, however the code is still accessible via the formspec.

If LuaControllers handle sensitive information, hacked clients could get this information from the LuaController. Marking the memory as private fixes this and saves a small amount of bandwidth.

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