Unit tests: Don't use OpenShot.h header (#607)

- To prevent slow compiles of unit tests, replace all of the
  '#include "OpenShot.h"' invocations with includes of the
  individual headers actually needed by each test file.

tests/Coordinate_Tests.cpp

@@ -31,9 +31,8 @@
 #include "UnitTest++.h"
 // Prevent name clashes with juce::UnitTest
 #define DONT_SET_USING_JUCE_NAMESPACE 1
-#include "OpenShot.h"
+#include "Coordinate.h"
 
-using namespace std;
 using namespace openshot;
 
 TEST(Coordinate_Default_Constructor)