Theme system

Solves #1

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

Depends on !21 (merged)

src/Lib/Log.cc

@@ -142,7 +142,7 @@ LogMessage::LogMessage(LogMessage &&other) noexcept
     , parentLogger(other.parentLogger)
 {
     std::memcpy(this, &other, sizeof(LogMessage));
-    std::memset(&other, 0, sizeof(LogMessage));
+    std::memset(reinterpret_cast<void *>(&other), 0, sizeof(LogMessage));
 }
 
 LogMessage &&