Add support for adding/editing/removing media captions. (#3547)

* Add support for editing media captions.

* Add composer snapshots.

* PR comment.

ElementX/Resources/Localizations/en.lproj/Localizable.strings

@@ -22,6 +22,7 @@
 "a11y_voice_message_record" = "Record voice message.";
 "a11y_voice_message_stop_recording" = "Stop recording";
 "action_accept" = "Accept";
+"action_add_caption" = "Add caption";
 "action_add_to_timeline" = "Add to timeline";
 "action_back" = "Back";
 "action_call" = "Call";
@@ -47,6 +48,7 @@
 "action_discard" = "Discard";
 "action_done" = "Done";
 "action_edit" = "Edit";
+"action_edit_caption" = "Edit caption";
 "action_edit_poll" = "Edit poll";
 "action_enable" = "Enable";
 "action_end_poll" = "End poll";
@@ -81,6 +83,7 @@
 "action_react" = "React";
 "action_reject" = "Reject";
 "action_remove" = "Remove";
+"action_remove_caption" = "Remove caption";
 "action_reply" = "Reply";
 "action_reply_in_thread" = "Reply in thread";
 "action_report_bug" = "Report bug";
@@ -119,6 +122,7 @@
 "banner_set_up_recovery_title" = "Set up recovery to protect your account";
 "common_about" = "About";
 "common_acceptable_use_policy" = "Acceptable use policy";
+"common_adding_caption" = "Adding caption";
 "common_advanced_settings" = "Advanced settings";
 "common_analytics" = "Analytics";
 "common_appearance" = "Appearance";
@@ -137,6 +141,7 @@
 "common_direct_chat" = "Direct chat";
 "common_edited_suffix" = "(edited)";
 "common_editing" = "Editing";
+"common_editing_caption" = "Editing caption";
 "common_emote" = "* %1$@ %2$@";
 "common_encryption" = "Encryption";
 "common_encryption_enabled" = "Encryption enabled";