Rename "pixels per step" to "steps per pixel"

I'm pretty sure the "pixels per step" label is incorrect and should actually read "steps per pixel".
Having looked at the code, the underlying variable is called csmRatio, which doesn't specify which way
round it should be. I think the minimal fix is to correct the label, which is what this commit does.

webapp/src/components/tabContentComponents/settingsComponents/CSMSettingsComponents/CSMCalibrationSettings.vue

@@ -42,7 +42,7 @@
             <matrixDisplay :matrix="csmResolution" :bracket-height="1.5" />
           </li>
 
-          <li>Pixels per motor step: {{ csmRatio }}</li>
+          <li>Motor steps per pixel: {{ csmRatio }}</li>
           <li>
             Full field of view in motor steps:
             <br />