Show button for trailers instead of card row (#618)

## Description
On both movie & series detail pages, show a button to play trailers
instead of the row of cards below.

The button works like this:
- If no trailers, the button shows "No trailers" and is
disabled/non-clickable
- If only a single trailer, the button shows "Play trailer" and clicking
it plays the trailer
- Otherwise, shows "Trailers" and clicking displays a dialog to choose
one

Local trailers are shown first in the list. Then there is an attempt to
sort the trailers for the dialog so that names with "Official Trailer"
or "Official Theatrical Trailer" are listed first and "Teaser" is listed
last. This isn't perfect and doesn't work for non-English, but there's
no other metadata to use.

### Related issues
Closes #408

app/src/main/res/values/strings.xml

@@ -399,6 +399,9 @@
     <string name="subtitle_delay">Subtitle delay</string>
     <string name="backdrop_display">Backdrop style</string>
     <string name="resolution_switching">Resolution switching</string>
+    <string name="local">Local</string>
+    <string name="play_trailer">Play trailer</string>
+    <string name="no_trailers">No trailers</string>
 
     <string-array name="theme_song_volume">
         <item>Disabled</item>