fbt: fixes (#1352)

* fbt: added --git-tasks; fixed typos
* fbt: fixed --extra-int-apps handling; scripts: moved storage.py & selfupdate.py to App() framework
* fbt: changed pseudo-builders to PhonyTargets with commands; added link to latest build dir as build/latest
* fbt: Restored old ep git handling
* fbt: dropped git tasks & dirlink.py
* fbt: removed extra quoting in fbt.cmd
* docs: added flash_usb to ReadMe.md

Co-authored-by: あく <alleteam@gmail.com>

fbt

@@ -2,11 +2,17 @@
 
 set -e
 
+SCRIPTDIR="$( dirname -- "$0"; )";
+SCONS_EP=${SCRIPTDIR}/lib/scons/scripts/scons.py
+
 if [[ -d .git ]]; then
-	echo "Updating git submodules"
-	git submodule update --init
+    echo Updating git submodules
+    git submodule update --init
+else # Not in a git repo
+    echo Not in a git repo, please clone with git clone --recursive
+    # Return error code 1 to indicate failure
+    exit 1
 fi
 
-SCRIPTDIR="$( dirname -- "$0"; )";
 SCONS_DEFAULT_FLAGS="-Q --warn=target-not-built"
-python3 ${SCRIPTDIR}/lib/scons/scripts/scons.py ${SCONS_DEFAULT_FLAGS} "$@"
+python3 ${SCONS_EP} ${SCONS_DEFAULT_FLAGS} "$@"