fbt: support for LOADER_AUTOSTART; post-build size stats (#1594)

* fbt: restored LOADER_AUTOSTART support
* scripts: added fwsize.py wrapper for size command; fbt: changed size post-build stats to fwsize.py call
* fbt: removed size wrapper
* fbt: added stats for binary flash size in pages
* fbt: hint on build options details
* scripts: fixed fwsize.py for *nix

applications/applications.h

@@ -18,6 +18,8 @@ typedef struct {
 
 typedef void (*FlipperOnStartHook)(void);
 
+extern const char* FLIPPER_AUTORUN_APP_NAME;
+
 /* Services list
  * Spawned on startup
  */