Project restructuring (fixes macOS builds) (#198)

- Create `Include/` folder for all main projects
- Fix some issues here and there (found while moving things)
- All includes are now in `Tactility/` subfolder and must be included with that prefix. This fixes issues with clashing POSIX headers (e.g. `<semaphore.h>` versus Tactility's `Semaphore.h`)

TactilityHeadless/Include/Tactility/service/ServiceManifest.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#include "Tactility/service/Service.h"
+
+#include <string>
+
+namespace tt::service {
+
+// Forward declarations
+class ServiceContext;
+
+typedef std::shared_ptr<Service>(*CreateService)();
+
+/** A ledger that describes the main parts of a service. */
+struct ServiceManifest {
+    /** The identifier by which the app is launched by the system and other apps. */
+    std::string id {};
+
+    /** Create the instance of the app */
+    CreateService createService = nullptr;
+};
+
+} // namespace