Merge branch 'master' into gameplay/devserver

Conflicts:
	src/gamelogic/game/g_admin.c
Tweak unlock thresholds for dev game.
Merge branch 'gameplay/viech' into gameplay/devserver
Merge branch 'master' into gameplay/devserver
Merge branch 'gameplay/master' into gameplay/viech
Add support for icons for buildings & classes.
Draw unlocked classes, weapons, upgrades and buildables.

This may extend beyond its allocated area; no clipping is done.
Vertical rendering has not been tested.
Rework unlockables display: show those initially locked, grouped by threshold.

Also adjust sizes and use the background colour for disabled items.

Items are shown in groups, using the full width (or height) of the box and
with equal spacing between groups.

Aligning the icons with the threshold marks leaves much more scope for
overlap; and with commit 91751a3 merged, they do indeed overlap unless
shrunk – which would leave them too small.
Merge branch 'gameplay/master' into gameplay/viech
Split crosshair indicator hit and friend/foe detection.
Tidy up build error tests a little.

* Combine no-build tests.
* Don't do team-specific checks if we already have a reason not to build.
* Always check whether the building would fit.
Make sure to check for no reactor/overmind (ghost buildable).
Implement status indicators for invalid building placement.

Various indicators are used. In some cases, emoticons are used to show
what's needed. Otherwise:
• the ‘unpowered’ icon (from the building health display) indicates when
  there's no reactor or overmind;
• “⧉” indicates that the building's bbox would intersect something else;
• “✕” indicates that the building would be in a no-build zone;
• “∡” indicates that the building would be on too steep a slope.
Improve mine rate display, fix overlapping with human inventory.
Give players credit minimum on spawn proportional to mine efficiency.
Merge branches 'gameplay/ds', 'ghost-indicate-reason' and 'gameplay/viech' into gameplay/devserver

Alien builder HUD is adjusted a little to fix an overlap due to changes in
both gameplay/ds and gameplay/viech.

Conflicts:
	main/ui/tremulous_human_hud.menu
Don't collect basic income when evolving.