Make AudioInputDialog and AudioOutputDialog use own icons.

Introduced config_audio_input.png and config_audio_output.png
for for that. Previously used config_basic.png.

Part of #1438
Drop unused files and icon.

Seems like we had some unreferenced files lying around.
- PAAudioConfig seems to be an (unfinished?) PulseAudio
  configuration dialog.
- PositionalSound seems to be an (unfinished?) positional
  audio configuration dialog.

They both used the config_dsound.png (directional? directsound?)
which this commit also drops as it doesn't seem to be used
anywhere.
Revert recent installer changes as they create more issues than they fixed.

This reverts commits e7282052993602ae5e0a1d3a8485c17adbf89d50
and 1749ef46dfc4c9ead4e41766ba9cace786f4fa35 .
Add placeholder texts to connect dialog.

Some users still try to enter a password in that dialog.
Try to make it even more clear what belongs in which field
by adding placeholder texts to the QLineEdits.

Hopefully fixes #1442
Shows move message if you moved a user from another channel into another channel
Show messages for priority speaker status
Add -limits to help text and improve man page
Update man pages author to "the Mumble team" and bump dates.
Translation update

Updating 'mumble_en.ts'...
    Found 1590 source text(s) (16 new and 1574 already existing)
Switch from fixing width to height for "What's this".

Done under the assumption that it is much more unlikely
a skin would attempt to create a very disproportionally
wide icon than a tall one.

Workaround part of #1438
Fix assert when viewing legacy user registration lists

This bug doesn't show up on release builds with QT4, I am not sure on
the effect on QT5 builds. When you connect a recent debug build to a
"legacy" server and view the user list, it will crash with the message:

ASSERT: "visual != -1" in file itemviews\qheaderview.cpp, line 1184

This is related to setting resize modes on columns that don't exist.
Transifex translation update

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Add ApplicationPalette class which allows theming the QApplication::palette.

Qt allows setting custom QPROPERTY values from QSS themes. As we cannot
style QPalettes this class has a property for each color group and
color role in a palette and acts as a stand-in for QApplication::palette
in the theme. When setting a qproperty-<group>-<role> on it in QSS
the brush will be set on the application palette.

The ApplicationPalette is derived from QWidget but never visible.
It listens to style changes on itself as those indicate the
application palette should be updated again. Variables not set
in the QSS will not be touched in the palette.

There might be some interactions with system style or theme changes
that have not yet been explored. Those are edge cases though and
can be fixed later.

ApplicationPalette.h is generated from ApplicationPaletteTemplate.h using
the generate-ApplicationPalette-class.py script. While it isn't expected
that this file has to change a lot in the future auto-generation is much
easier than writing all that boilerplate from hand.

Fixes #1438
Integrate some feedback to ApplicationPalette

* Changed naming scheme from "qproperty-<group>_<role>"
  to "qproperty-<role>_<group>".
* Introduced "qproperty-<group>" to set all roles of the
  group to the same brush
Fix more ApplicationPalette aspects.

* Getters actually have to be working
* Have to be able to reset palette parts that
  aren't overridden by theme.
* Add search folder when setting theme
Transifex translation update
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