Add language dropdown to compose view (#2651)

* Add UI for selecting post language

* Apply selected language when sending status

* Save/restore post language with drafts

* Fall back to english if the configured language isn't found in the locale list (no-NB)

* Remove comment about no_NB

* Move language dropdown to top of compose view

* Preserve language when redrafting

* Set default language to target post's language when replying

* Add Tusky license header to new source file

* Tweak language dropdown button width

app/src/main/java/com/keylesspalace/tusky/entity/Status.kt

@@ -48,7 +48,8 @@ data class Status(
     val pinned: Boolean?,
     val muted: Boolean?,
     val poll: Poll?,
-    val card: Card?
+    val card: Card?,
+    val language: String?,
 ) {
 
     val actionableId: String
@@ -130,7 +131,8 @@ data class Status(
             sensitive = sensitive,
             attachments = attachments,
             poll = poll,
-            createdAt = createdAt
+            createdAt = createdAt,
+            language = language,
         )
     }