Refactoring, housekeeping, documentation

Add a class diagram. Still needs some details.
Refactor to better respect SOLID principles.
Housekeeping, move and rename classes/files.

app/src/ConfigManager.cxx

@@ -0,0 +1,29 @@
+#include <filesystem>
+#include <fstream>
+
+#include <ConfigManager.h>
+#include <memory>
+
+using namespace std;
+namespace fs = std::filesystem;
+
+ConfigManager::ConfigManager() {
+  if (fs::exists(CONFIG_FILE)) {
+    ifstream f(CONFIG_FILE);
+    mConfig = json::parse(f);
+  }
+}
+
+void ConfigManager::SaveFans(vector<shared_ptr<Fan>> fans) {
+  json obj;
+
+  for (auto fan : fans) {
+  }
+}
+
+ConfigManager::~ConfigManager() { WriteConfig(); }
+
+void ConfigManager::WriteConfig() {
+  ofstream f(CONFIG_FILE, ios::trunc);
+  f << mConfig.dump(2) << endl;
+}