Work towards #123 adaptive bitrate

Not complete but some useful changes to bitrate code so merged anyway. ABR disabled for now since it needs tuning and a better way of knowing when the bitrate change has actually taken effect.

components/rgbd-sources/src/abr.cpp

@@ -13,7 +13,7 @@ using ftl::rgbd::detail::NetFrame;
 
 ABRController::ABRController() {
     bitrate_ = 0;
-    enabled_ = true;
+    enabled_ = false;
     max_ = kBitrateBest;
     min_ = kBitrateWorst;
 }
@@ -33,7 +33,7 @@ void ABRController::setMinimumBitrate(bitrate_t b) {
 }
 
 void ABRController::notifyChanged() {
-    enabled_ = true;
+    //enabled_ = true;
 }
 
 bitrate_t ABRController::selectBitrate(const NetFrame &frame) {