Big code refactor

The design was defective and I didn't expect the popularity of the project. After these changes the code will be more mantainable and understandable.

Among the changes we can see:
- A better code structure
- Decoupled button widget from its logic
- More code reuse
- Easier way to add buttons
- Specialized classes

src/main.cpp

@@ -25,7 +25,6 @@
 #include <QDBusMessage>
 #include <QCommandLineParser>
 #include <QDir>
-#include <QDebug>
 
 int main(int argc, char *argv[]) {
     QTranslator translator;