implement user preference for elevation plots starting at zero;

add docker make command to downgrade db;
add (google-powered) translations for the new labels

fittrackee_client/src/locales/en/common.json

@@ -5,6 +5,7 @@
     "DAY": "day | days",
     "DISPLAYED": "Displayed",
     "DOCUMENTATION": "documentation",
+    "FALSE": "False",
     "HERE": "here",
     "HIDDEN": "Hidden",
     "HOME": "Home",
@@ -21,5 +22,6 @@
             "LABEL": "par page"
         }
     },
-    "TOTAL": "Total"
+    "TOTAL": "Total",
+    "TRUE": "True"
 }

fittrackee_client/src/locales/en/user.json

@@ -92,6 +92,7 @@
             "STOPPED_SPEED_THRESHOLD": "stopped speed threshold"
         },
         "SPORTS_EDITION": "Sports preferences edition",
+        "START_ELEVATION_AT_ZERO": "Start elevation plots at zero",
         "SUCCESSFUL_EMAIL_UPDATE": "Your account has been updated successfully. Please check your email to confirm your new email address.",
         "SUCCESSFUL_REGISTRATION": "Your account has been created successfully.",
         "SUCCESSFUL_REGISTRATION_WITH_EMAIL": "A link to activate your account has been emailed to the address provided.",