Basic UI: Signal resize of properties view

If the properties view changed in the properties window, the viewport of
the properties would not trigger a resize because the size of the window
itself does not change.  This creates a signal that allows the parent to
know whether or not to update a viewport, if any.
win-dshow: Change a few functions to static/inline
Update win-dshow to latest libdshowcapture ver

This makes win-dshow use the new std::function callbacks instead of the
old C-style callbacks.
Handle audio channels correctly in pulseaudio plugin

This fixes a bug where the pulseaudio plugin always reported
a speaker layout of stereo to obs, regardless of how many channels
pulseaudio actually recorded.
If the default number of channels was different to 2 this would
cause audio distortion.
Merge pull request #260 from fryshorts/pulse-input

Handle audio channels correctly in pulseaudio plugin
Fix bug with source audio

If the audio didn't start at the 0 timestamp, it would misinterpret it
as a timestamp jump because obs_source::next_audio_ts_min is set to 0 on
creation.  Timestamp starting values should be allowed to start at any
arbitrary value.
win-dshow: Add audio support

This implements audio support, allowing not only the ability to capture
the built-in audio from the video device's audio capture pin, but also
the ability to override the default audio with a custom audio device.

The DShowInput::Update function was split up and refactored a bit, as it
was getting a bit large and messy.
Basic UI: Reduce audio meter mute timing threshold

Some devices burst their audio (such as when querying audio from
directshow), and the 250 millisecond threshold that sets the audio meter
back to muted status would erroneously cause the meter to appear bounce
back between muted and unmuted.  Instead, a one second test should be
sufficient time to prevent that from happening.