implemented speed/duration dialog and most of its functionality

An earlier commit implementing media in and out parameters was primarily for
this addition. A simple control dialog for the clip's speed presentation
reimplemented from the old codebase.

app/common/rational.cpp

@@ -9,6 +9,12 @@ rational::rational(const AVRational &r) :
 {
 }
 
+rational rational::fromDouble(const double &flt)
+{
+  // Use FFmpeg function for the time being
+  return av_d2q(flt, INT_MAX);
+}
+
 //Function: print number to cout
 
 void rational::print(ostream &out) const

app/common/rational.h

@@ -55,6 +55,8 @@ public:
 
   rational(const AVRational& r);
 
+  static rational fromDouble(const double& flt);
+
   //Assignment Operators
   const rational& operator=(const rational &rhs);
   const rational& operator+=(const rational &rhs);