Theme system

Solves #1

Can choose between QtCreator's themes and base Vivy theme, or system's theme.

Depends on !21 (merged)

src/Lib/Utils.hh

@@ -17,10 +17,15 @@
                                        ", line " VIVY_ASSERT_STRINGIFY(__LINE__))
 
 #define VIVY_GUARD(cond) ((Q_LIKELY(cond)) ? true : (VIVY_ASSERT_STRING(#cond), false))
-#define VIVY_UNUSED      __attribute__((unused))
-#define VIVY_EXPORT      __attribute__((visibility("default")))
-#define VIVY_NO_EXPORT   __attribute__((visibility("hidden")))
-#define VIVY_DEPRECATED  __attribute__((__deprecated__))
+#define VIVY_ASSERT(cond)              \
+    {                                  \
+        if (!cond)                     \
+            VIVY_ASSERT_STRING(#cond); \
+    }
+#define VIVY_UNUSED     __attribute__((unused))
+#define VIVY_EXPORT     __attribute__((visibility("default")))
+#define VIVY_NO_EXPORT  __attribute__((visibility("hidden")))
+#define VIVY_DEPRECATED __attribute__((__deprecated__))
 
 // Use chrono instead of std::chrono...
 namespace chrono = std::chrono;