fix(api) invert filmstrip autohide flag

config.js

     //     'transcribing.failedToStart' // shown when transcribing fails to start
     // ],
 
-    // Automatically hides the filmstrip when screen width is under a certain threshold
-    autohideFilmstrip: true,
+    // Prevent the filmstrip from autohiding when screen width is under a certain threshold
+    // disableFilmstripAutohiding: false,
 
     // Allow all above example options to include a trailing comma and
     // prevent fear when commenting out the last value.

react/features/base/config/configWhitelist.js

     'analytics.disabled',
     'audioLevelsInterval',
     'audioQuality',
-    'autohideFilmstrip',
     'apiLogLevels',
     'avgRtpStatsN',
     'backgroundAlpha',
     'disableAP',
     'disableAudioLevels',
     'disableDeepLinking',
+    'disableFilmstripAutohiding',
     'disableInitialGUM',
     'disableH264',
     'disableHPF',

react/features/filmstrip/subscriber.web.js

     /* selector */ state => state['features/base/responsive-ui'].clientWidth < ASPECT_RATIO_BREAKPOINT,
     /* listener */ (widthBelowThreshold, store) => {
         const state = store.getState();
-        const { autohideFilmstrip } = state['features/base/config'];
+        const { disableFilmstripAutohiding } = state['features/base/config'];
 
-        if (autohideFilmstrip) {
+        if (!disableFilmstripAutohiding) {
             store.dispatch(setFilmstripVisible(!widthBelowThreshold));
         }
     });