Update docs and fix bugs (#149)

Improved the docs for the 3 main Tactility projects. I also fixed some inaccuracies and bugs in certain APIs as I went through the code.

Tactility/Source/app/ManifestRegistry.h

@@ -6,8 +6,16 @@
 
 namespace tt::app {
 
+/** Register an application with its manifest */
 void addApp(const AppManifest* manifest);
+
+/** Find an application manifest by its id
+ * @param[in] id the manifest id
+ * @return the application manifest if it was found
+ */
 const AppManifest _Nullable* findAppById(const std::string& id);
+
+/** @return a list of all registered apps. This includes user and system apps. */
 std::vector<const AppManifest*> getApps();
 
 } // namespace