add the block switching string

Author: jwklong

src/addons/addons-l10n/en.json

@@ -156,6 +156,7 @@
     "block-switching/control_if": "if",
     "block-switching/control_if_else": "if... else",
     "block-switching/control_repeat_until": "repeat until",
+    "block-switching/control_while": "while",
     "block-switching/control_wait_until": "wait until",
     "block-switching/data_changevariableby": "change variable",
     "block-switching/data_deletealloflist": "delete all",