viewer: implemented basic deinterlace

Implements a very basic GLSL deinterlace that simply halves the vertical
resolution and then interpolates between the fields. This can be toggled
on or off.

The reasons for being so basic is:
- Speed, very quick code running in OpenGL
- It would seem the highest quality deinterlacers are temporally based
  which doesn't make much sense for the viewer, particularly since we can't
  double the frame rate since our timecode is fixed to the frames.

Higher quality interlacing/deinterlacing will be present in the actual
renderer.

app/widget/viewer/viewerdisplay.cpp

@@ -43,7 +43,8 @@ ViewerDisplayWidget::ViewerDisplayWidget(QWidget *parent) :
   signal_cursor_color_(false),
   gizmos_(nullptr),
   gizmo_click_(false),
-  last_loaded_buffer_(nullptr)
+  last_loaded_buffer_(nullptr),
+  deinterlace_(false)
 {
 }
 
@@ -86,6 +87,12 @@ void ViewerDisplayWidget::SetImage(FramePtr in_buffer)
   update();
 }
 
+void ViewerDisplayWidget::SetDeinterlacing(bool e)
+{
+  deinterlace_ = e;
+  update();
+}
+
 const ViewerSafeMarginInfo &ViewerDisplayWidget::GetSafeMargin() const
 {
   return safe_margin_;
@@ -212,6 +219,12 @@ void ViewerDisplayWidget::paintGL()
     // Bind retrieved texture
     f->glBindTexture(GL_TEXTURE_2D, texture_.texture());
 
+    // Set some parameters
+    color_service()->pipeline()->bind();
+    color_service()->pipeline()->setUniformValue("ove_resolution", texture_.width(), texture_.height());
+    color_service()->pipeline()->setUniformValue("ove_deinterlace", deinterlace_);
+    color_service()->pipeline()->release();
+
     // Blit using the color service
     color_service()->ProcessOpenGL(true, matrix_);