Approach consistent filmstrip naming

We seemed to be using the names "film strip" and "filmstrip" (and,
consequently, their source code-conscious forms such as film-strip,
FilmStrip, etc.) In order to comply with our coding style which requires
a consistent one name for a given abstraction, choose one name and
rename the uses of the other name.

Wikipedia has a definition of a "filmstrip", I couldn't find a "film
strip". I guess our abstraction can be seen as what's described there.
When I google "film strip", I get results about "filmstrip" at the top.
That's why I chose "filmstrip".

Certain uses of "film strip" such as interfaceConfig.filmStripOnly and
in the external API I left untouched in an attempt to preserve
compatibility.

I wasn't sure whether CSS was tangled in compatibility so I made a
choice and renamed there was well.

modules/API/API.js

@@ -49,7 +49,7 @@ function initCommands() {
             APP.conference.changeLocalDisplayName.bind(APP.conference),
         "toggle-audio": APP.conference.toggleAudioMuted.bind(APP.conference),
         "toggle-video": APP.conference.toggleVideoMuted.bind(APP.conference),
-        "toggle-film-strip": APP.UI.toggleFilmStrip,
+        "toggle-film-strip": APP.UI.toggleFilmstrip,
         "toggle-chat": APP.UI.toggleChat,
         "toggle-contact-list": APP.UI.toggleContactList,
         "toggle-share-screen":

modules/API/external/external_api.js

@@ -337,7 +337,7 @@ class JitsiMeetExternalAPI extends EventEmitter {
      * passed in the arguments array.
      * toggleAudio - mutes / unmutes audio with no arguments.
      * toggleVideo - mutes / unmutes video with no arguments.
-     * filmStrip - hides / shows the film strip with no arguments.
+     * toggleFilmStrip - hides / shows the filmstrip with no arguments.
      * If the command doesn't require any arguments the parameter should be set
      * to empty array or it may be omitted.
      *
@@ -362,7 +362,7 @@ class JitsiMeetExternalAPI extends EventEmitter {
      * passed in the arguments array.
      * toggleAudio - mutes / unmutes audio. no arguments
      * toggleVideo - mutes / unmutes video. no arguments
-     * filmStrip - hides / shows the film strip. no arguments
+     * toggleFilmStrip - hides / shows the filmstrip. no arguments
      * toggleChat - hides / shows chat. no arguments.
      * toggleContactList - hides / shows contact list. no arguments.
      * toggleShareScreen - starts / stops screen sharing. no arguments.