[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/examples/blink.c

@@ -12,7 +12,7 @@ void rgb_set(
     gpio_write(led_b, !b);
 }
 
-void application_blink(void* p) {
+int32_t application_blink(void* p) {
     // TODO open record
     const GpioPin* led_r_record = &led_gpio[0];
     const GpioPin* led_g_record = &led_gpio[1];
@@ -41,4 +41,6 @@ void application_blink(void* p) {
         rgb_set(0, 0, 0, led_r_record, led_g_record, led_b_record);
         delay(500);
     }
+
+    return 0;
 }