Make base_anim.nif take priority for biped creatures

Fixes the skeletal minion's WalkForward1h animation.
Don't add combat AI to player
Take actor's speed into account in stuck check

The Winged Twilight's walking animation was so slow that it incorrectly detects being stuck.
Remove redundant isHostile flag (Fixes #1652)
Reset player position when spawning in fallback cell
Adjust AiFollow running threshold to more closely match vanilla MW
Don't make guards fight non-aggressive creatures that are in combat

Ex. summoned creature that is helping in a fight.
Sheath weapon in all Ai packages except for AiCombat
Remove defunct option for building without FFmpeg

- Added REQUIRED to find_package(FFmpeg)
- Removed USE_FFMPEG option from CMakeLists.txt
- Always use FFmpeg for sound input
- Removed SOUND_DEFINE from CMakeLists.txt
- Removed #else branch from videoplayer.cpp with dummy VideoState code
  (FFmpeg is now guaranteed to exist and the code was incomplete)
- Remove #ifdef OPENMW_USE_FFMPEG in ffmpeg_decoder.cpp, it is guaranteed to be used
- Remove #ifdef OPENMW_USE_FFMPEG from soundmanagerimp.cpp, it is guaranteed to be used
Only show "target resists magic" message for spells cast by player
Cancel upper body animations when knocked down
updated credits file
Fix http://bugs.openmw.org/issues/768

Changes application_name in configuration manager to OpenMW instead of
openmw, if on windows. This shouldn't break anything since Windows uses
case-insensitive filesystems. Strictly speaking the installation
directory must be OpenMW now though (not sure whether this is the case)
Support loading text keys for objects without a skeleton

This means we can no longer map them to bone IDs, but they are unused anyway.

Required to load text keys from the default head models (such as Talk: Start/Stop and Blink: Start/Stop)
AI tell their greatings even when player is moving (like morrowind).
Greating reset distance was greatly inflated comparing with morrowind.
Implement AI greeting states.

Greeting consist of 3 phases:
- none - default one, greeting state can only change to "in progress"
  when near enough and some time passes
- in progress - NPC says his greating and rotates toward player,
  state can only change to "done" after some time
- done - rotation is stoped, after idling can go away from player,
  state can only change to "none" when player and NPC are faraway
Add grace periods for player greeting.

Add delay for NPC greating. NPC ignores greeted player after some time.
Fixes bug 1503.
Implement mouth animation for NPCs based on say sound (Fixes #642)
Implement NPC eye blinking (Fixes #1721)
Merge remote-tracking branch 'funkybit/master'