Hungarian translation update by mtomi78.

Closes #3966, #3969, #3973, #4000.
Update zlib to 1.2.8 for the mac builds.
Update png to 1.5.15 for the mac builds.
Simplified Chinese translation update by Peng.

Closes #4017.
Do not allow Nexus AI to build hardened sensor towers before being researched.

Fixes ticket:4025.
Make VTOLs return to rearm when out of ammo, if told to patrol or circle.

However, if set to hold fire, don't return to rearm, even when reaching a patrol endpoint.

Fixes ticket:3705.
Add Shift+V to select all fully-armed VTOLs.
Simplify droid selection type code.
When entering a map name, sort maps by some kind of similarity to the entered map name.

Previous behaviour was to ignore the entered map name, and reset it. This meant that typing a map name was actually
somewhat futile.
Stop and disconnect derricks when starting to demolish.

Fixes ticket:3176.
Fix completely broken effectStructureUpdates() and remove redundant variable RES_EXTRACTOR::active.

The best part of effectStructureUpdates() was using the same variable i as an inner and outer loop variable, even
though the inner loop didn't actually do anything (except changing i).
Fix wall alignment with fortresses.

Take into account the 2×2 size.

Fixes ticket:1520 and ticket:3236.
Make waiting-at-HQ units go to newly-built repair facilities or rearming pads.

Fixes ticket:3105.
Fix off-by-one error in setOverrideMods (strlcpy copies n-1 bytes). Fixes ticket:3567.
identity: Give players unique unspoofable player IDs.

Players generate private keys (stored in the .sta files). Replies to NET_PING are now signed, so if the ping of a
player is not ∞, and you recognise the player ID of the player, then you know the ping is from the same player as
before.
identity: Show players in different colours, depending on whether the player was seen before or is lagging.

Also, don't start the game if a player is lagging, since in that case, the game might anyway not actually start
until the player finally times out.
identity: Add libcrypto to configure.ac/Makefile.am.

Apparently needs to be explicitly linked, for the buildbot.
identity: Add libcrypto to the mac builds.
Update png for mac builds to 1.5.16.
Update nullbot to v2.05.