GlobalShortcutWin: try to make WinHooks do less work.

This change switches GlobalShortcutWin over to a slightly different model
in an attempt to combat the WinHook timeouts users have been reporting.

Previously, the DirectInput poller and the WinHooks event handling lived in
the same high-priority thread, and both of them processed all incoming button
events. Since both of them processed all events and emitted them using
GlobalShortcutEngine's handleButton method, they had to live in the same
thread in order for us to control the order of the signal dispatch.

Having the WinHooks live in the same thread as the DirectInput polling meant
that the hooks could potentially be blocked every 20 ms by the DirectInput
poller's timer event, which wasn't really desirable.

This new model splits up the DirectInput poller and the WinHooks event handling
into two separate, high-priority threads, each with different responsibilities.

The DirectInput poller is now the main source of events. This is where the actual
global shortcut presses are handled. Having DirectInput responsible for all
global shortcut buttonUp and buttonDown events allows us to use the WinHooks
thread *just* for filtering suppressed keys.

This design allows our WinHooks to have their own thread and event loop, meaning
they won't have to fight the DirectInput polling timer. Also, since the WinHooks
now have a more restricted set of tasks, they're able to do less work, hopefully
making it harder to trigger a timeout.
GlobalShortcutWin: revert 242af40b to restore keyboard suppression.

When our WH_KEYBOARD_LL hook suppressed keypresses, DirectInput couldn't
read them.

Let's revisit this optimization for 1.2.5. We can always refer users
having issues with hook timeouts to the registry hack.
setLiveConf for opusthreshold and channelnestinglimit didn't reset on
empty string (#938)
Minor fixes for French translation
mumble_da.ts: 3. part licenser -> Tredjepartslicenser.
mumble_sv.ts: update for 1.2.4.
mumble_ja.ts: mark as finished.
mumble.pro: exclude unfinished NL translation.
mumble.qrc: also remove NL from here.
mumble.pro, mumble.qrc: remove unfinished Hebrew translation from release.
mumble.pro, mumble.qrc: remove unfinished Hungarian translation from release.
mumble_qt.qrc: remove nl, he, hu.
Introduce concept of NULL plugin to retract plugins.

* NULL plugins have a shortname of L"Retracted" which excludes them
  from being listed as a plugin in Mumble >= 1.2.4
* NULL plugins are valid plugins that always return false on trylock
  so Mumble <= 1.2.3 gets behavior close to what recent Mumble has.
* NULL css, dods, tf2 and hl2dm plugins as they have been replaced by link support in the source engine.
Default disable hide in tray also for Windows 8

* Can't use os_win.cpp versioning code as global settings singleton
  is initialized before os_init() routine populates variables.
* For now went with the option with least code impact. This should
  be revisited after release.
Update changelog and LICENSE file.

* Nonfunctional commit
Merge remote-tracking branch 'upstream/master' into positional_audio