Prevent already failed objectives from being marked as completed

The same change was not and must not be done in the reverse case. It
should be and is possible to mark an already completed objective as
failed.

Consider a case where a player is supposed to capture, but not destroy,
a building.  He captures it, the objective is complete.  However, later
in the game that building gets destroyed. In this case, the objective
should be changed to failed.
Allow canceling beacons with right click
Merge pull request #6506 from abcdefg30/beaconcancel

Allow canceling beacons with right click
Create Mods.Common

Create a small base for Mods.Common and update solution and makefile to use it
Update third party Windows DLLs

http://kcat.strangesoft.net/openal-soft-1.16.0-bin.zip
Merge pull request #6513 from steelphase-forks/windows-dll-update

Fixes #6508
Remove beacons when the badgers get shot down
Add more functions for objectives management to Lua API
Update existing maps
Merge pull request #6505 from abcdefg30/beaconfix

Remove beacons when the badgers get shot down
Move inaccuracy modifier queries outside the projectile ctors. Fixes #6449.
Add a chat tab to end-game window

Fixes #6422
Remove stats button from end-game dialog in mission-type maps

Still available for skirmish games and replays.
Merge pull request #6510 from pchote/fix-inaccuracy-crash

Move inaccuracy modifier queries outside the projectile ctors.
Merge pull request #6511 from steelphase-forks/bleed

Creation of Mods.Common.
Merge pull request #6494 from obrakmann/objectives-fine-tuning

Objectives fine-tuning
Merge pull request #6473 from obrakmann/fix6422

Add chat tab to end-game dialog
Polishing/normalizing new GUI
Merge pull request #6518 from s1ww/player_gui

Polishing/normalizing new GUI