implemented a footage viewer

Essentially a minor derivation of a viewer type that can automatically view
footage from the project (i.e. not in a sequence).

app/project/item/footage/audiostream.cpp

@@ -42,12 +42,12 @@ void AudioStream::set_channels(const int &channels)
   channels_ = channels;
 }
 
-const uint64_t &AudioStream::layout()
+const uint64_t &AudioStream::channel_layout()
 {
   return layout_;
 }
 
-void AudioStream::set_layout(const uint64_t &layout)
+void AudioStream::set_channel_layout(const uint64_t &layout)
 {
   layout_ = layout;
 }

app/project/item/footage/audiostream.h

@@ -37,8 +37,8 @@ public:
   const int& channels();
   void set_channels(const int& channels);
 
-  const uint64_t& layout();
-  void set_layout(const uint64_t& layout);
+  const uint64_t& channel_layout();
+  void set_channel_layout(const uint64_t& channel_layout);
 
   const int& sample_rate();
   void set_sample_rate(const int& sample_rate);