[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/sd-nfc/sdnfc.cpp

@@ -161,7 +161,8 @@ void AppSdNFC::blink_green() {
 }
 
 // app enter function
-extern "C" void sdnfc(void* p) {
+extern "C" int32_t sdnfc(void* p) {
     AppSdNFC* app = new AppSdNFC();
     app->run();
+    return 0;
 }