[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/cli/cli.c

@@ -172,7 +172,7 @@ void cli_add_command(Cli* cli, const char* name, CliCallback callback, void* con
     string_clear(name_str);
 }
 
-void cli_task(void* p) {
+int32_t cli_task(void* p) {
     Cli* cli = cli_alloc();
 
     // Init basic cli commands
@@ -184,4 +184,6 @@ void cli_task(void* p) {
     while(1) {
         cli_process_input(cli);
     }
+
+    return 0;
 }