Restructure "src/" folder

Moving files from the "src/" folder into "src/legacy", "src/macro-core",
and "src/utils" was necessary as it was becoming a bit too cluttered.

src/platform-funcs.hpp

@@ -0,0 +1,19 @@
+#pragma once
+#include "hotkey.hpp"
+
+#include <vector>
+#include <string>
+#include <QStringList>
+
+void GetWindowList(std::vector<std::string> &windows);
+void GetWindowList(QStringList &windows);
+void GetCurrentWindowTitle(std::string &title);
+bool isFullscreen(const std::string &title);
+bool isMaximized(const std::string &title);
+std::pair<int, int> getCursorPos();
+int secondsSinceLastInput();
+void GetProcessList(QStringList &processes);
+bool isInFocus(const QString &executable);
+void PressKeys(const std::vector<HotkeyType> keys, int duration);
+void PlatformInit();
+void PlatformCleanup();