Also don't show "probably running a different version" message in simple singleplayer mode

Improve TOCLIENT_ACTIVE_OBJECT_MESSAGES robustness for handling invalid data

Add serializeHexString()
Clean up util/serialize.cpp

Fix 'is ground content' for some nodes

- Stop attempting to start a world when no world's created/selected in server tab
- Better world's indexes handling between subgames lists

Spare some copies.

The neighbours checked are the 8 nodes horizontally surrounding the decoration base
and the 8 nodes horizontally surrounding the ground node below the decoration

Use wide_to_utf8 and utf8_to_wide instead of wide_to_narrow and narrow_to_wide at almost all places.
Only exceptions: test functions for narrow conversion, and chat, which is done in a separate commit.

- Fixed race conditions
- Fixed null dereference
- Fixed out-of-bounds array access
- MinimapMapblock is now allocated and added to update queue only when enabled
- Removed dependency on LocalPlayer
- Fixed code style
- Simplified expressions and program logic
- Cleaned minimap object interfaces

Lowest level of base terrain determines mountain generation in mapchunk
Change some positional function arguments from int to s16

Previously, m_proto_ver was set to the serialisation version
inside the legacy init packet.

Now, if the server doesn't send a protocol version (protocols < 25),
we set m_proto_ver to some value < 25 and > 0.

Use numbers instead of iterators to traverse various vectors.

Previously, if you did `make envpaths` (as described in README.android), the new file got listed by git as new file.

@RealBadAngel has removed all outside access of the cache.