This reduces the PNG file sizes and fixes the invalid sRGB profile warnings.
I have additionally reduced the moremesecons_luablock.png resolution to 32x32.
Data associated to a LuaBlock is redundantly stored in both its metadata
and in the mod storage so that it is not possible to hack a LuaBlock by
changing its metadata or copying it using WorldEdit. This commit changes
how it is done:
* Store full code instead of storing MD5 checksum, which avoids bug
caused by serializing non-ASCII strings using minetest.serialize,
* Also store owner,
* Use `minetest.hash_node_position` instead of deprecated vector_extras
set_data_to_pos etc,
* Remove mod storage data associated with the LuaBlock when destroying
it,
* Create helper functions for manipulating the mod storage in
moremesecons_utils, I will soon update other parts of MoreMesecons as well to use them.
This commit breaks backwards compatibility: previously created LuaBlocks
will have to be reset by opening the formspec and pressing the `Submit`
button.
This commit also fixes an unrelated bug: code in the formspec was not
correctly escaped using minetest.formspec_escape.
