[FL-872] Furi, API-HAL, App-Loader cleanup and improvements (#334)

* Furi: replace obsolete furiac_exit with osThreadExit, drop obsolete apis and test. Rename systemd to flipper and move to separate file, cleanup. ApiHal: Rename timebase to os and move freertos hooks there, move insomnia api to power module.
* Furi: new thread helper
* Furi: cleanup thread documentation
* Flipper, AppLoader: update to use FuriThread. Update tasks signatures to match FuriThreadCallback signature.
* F4: rename API_HAL_TIMEBASE_DEBUG to API_HAL_OS_DEBUG
* Applications: rename FuriApplication to FlipperApplication, use FuriThreadCallback signature for apps.
* C++ app template sample, new exit method

applications/input/input.c

@@ -18,7 +18,7 @@ void input_isr(void* _pin, void* _ctx) {
     osThreadFlagsSet(input->thread, INPUT_THREAD_FLAG_ISR);
 }
 
-void input_task() {
+int32_t input_task() {
     input = furi_alloc(sizeof(Input));
     input->thread = osThreadGetId();
     init_pubsub(&input->event_pubsub);
@@ -69,4 +69,6 @@ void input_task() {
             osThreadFlagsWait(INPUT_THREAD_FLAG_ISR, osFlagsWaitAny, osWaitForever);
         }
     }
+
+    return 0;
 }