Fix for bug 1196.

This bug would cause the player to jump when jump was assigned to
Space and they closed a dialog with Space. I tested vanilla
MW for behaviour and found that Jump was the only basic input which
MW does not allow when closing dialogs (i.e. if Space is assigned to
move forward, MW will move you forward after closing the dialog).

There were two reasons for the bug:
1) OpenMW GUI does not consume UI events
2) Jump occurs so long as key is down (not only on first key down)

To minimally fix the bug, I made it so that keypress events can be
consumed by the GUI and not passed along to the player control
input manager (1). However, if the player holds space, they will still
jump (as the subsequent key held events will be captured and cause
a jump).

Unfortunately, there is no idiomatic way that I could find in the
OpenMW input manager to perform events only on key down. Instead,
I introduced a variable which tracks whether the jump key has been
pressed for the first time within the current frame (2).

Note: I was initially concerned that limiting the jump event to
KeyDown and not Key Hold would cause issues with swimming,
levitating, or variable height jumping. However, after a bunch
of testing in vanilla MW and exploration of the OpenMW codebase
I could find nothing suggesting the need to capture the jump
key being held.
Small fix for menu background
Loop main menu video when it's finished playing
Fix several edit boxes not receiving mouse input
Update in response to comments.

It turns out I was erroneous about problem (1) in my original commit
message. I thought that in an edge case the OpenMWGUI could both handle
the same event on the frame the GUI was closed. My test for
this was broken. So after brainstorming many possible unsatisfactory
solutions to this event handling, it's luckily not necessary!
Merge DialInfo objects by subrecord instead of overwriting the object

Fixes #1360
Fix unhandled edge case in TradeItemModel with items that are able to stack, but are not currently stacked (e.g. after repairing a damaged item)

Fixes #1368
Make trade balance label editable
Make trade disposition changes temporary again, as in vanilla
Fix trade exploit

Using the Max Sale button it was possible to "invert" the buying/selling state.
Fix errors due to BaseWhite material being removed
When dialogue goodbye is forced, allow using either the red link or the goodbye button

Fixes #1373
1196/1217 fix

Fixes an issue where inputs could be processed by both GUI and
gameplay systems. An enabled/disable has been added to OIS
channels, and OpenMW now disables player gameplay hotkeys when
a GUI element has focus. GUI hotkeys are left enabled.
Merge branch 'master' into bug1196jumpdialog

Conflicts:
	apps/openmw/mwinput/inputmanagerimp.cpp
Addition to 7c9c0830a96: don't create useless BaseWhite clones
Merge remote-tracking branch 'scrawl/master'
Fix loading a savegame when some of its content files were disabled

Fixes #1380
Respect CMAKE_INSTALL_PREFIX in the global openmw.cfg

Fixes installing to /usr/local (Bug #1378)
Fix Bug #1371

Not properly reading in the NIF file's QuaternionKeyList.
Fix CMake scripts to link static dependencies

Added FindDirectX scripts from Ogre so that FindOgre.cmake doesn't
fail silently to find the libraries correctly.

Modified top-level CMakelists.txt:
- Correctly set include dirs, preprocessor definitions, and add
  libraries for static Ogre plugins.
- Correctly set preprocessor definitions for static MyGUI.

Modified launcher, openmw, and opencs to link the static Ogre plugins.

Fixed FindSDL2.cmake to set a variable that contains only the SDL2
library, so that the launcher doesn't incorrectly link against
SDL2main.

Fixed FindMyGUI.cmake to correctly look for static variants.

Fixed FindOgre.cmake to set variables for DirectX plugins correctly.