Added support for Fraunhofer / TeleOrbit Flexiband front-end

demultiplexed signal files (interleaved I/Q byte-size files,
post-process only).

Use sample configuration file gnss-sdr_Hybrid_byte.conf to try it!

Go to http://www.iis.fraunhofer.de/de/ff/lok/leist/test/flexiband.html
to obtain free captures from Fraunhofer

src/algorithms/signal_source/adapters/file_signal_source.cc

@@ -83,6 +83,10 @@ FileSignalSource::FileSignalSource(ConfigurationInterface* configuration,
         {
             item_size_ = sizeof(short int);
         }
+    else if (item_type_.compare("byte") == 0)
+        {
+    		item_size_ = sizeof(char);
+        }
     else
         {
             LOG(WARNING) << item_type_