Use "screen/tab casting" instead of "mirroring"

CONTRIBUTING.md

@@ -24,11 +24,27 @@ https://lusito.github.io/web-ext-translator/?gh=https://github.com/hensm/fx_cast
 
 Missing/outdated strings:
 
+* `de`
+    * `optionsMirroringCategoryName`
+    * `optionsMirroringCategoryDescription`
+    * `optionsMirroringEnabled`
+    * `optionsMirroringAppId`
+
+* `es`
+    * `optionsMirroringCategoryName`
+    * `optionsMirroringCategoryDescription`
+    * `optionsMirroringEnabled`
+    * `optionsMirroringAppId`
+
 * `nl`
     * `optionsBridgeBackupEnabled`
     * `optionsUserAgentWhitelistRestrictedEnabled`
     * `optionsUserAgentWhitelistRestrictedEnabledDescription`
     * `optionsOptionRecommended`
+    * `optionsMirroringCategoryName`
+    * `optionsMirroringCategoryDescription`
+    * `optionsMirroringEnabled`
+    * `optionsMirroringAppId`
 
 
 ### NSIS Installer Localization

ext/src/_locales/en/messages.json

@@ -362,19 +362,19 @@
     }
 
   , "optionsMirroringCategoryName": {
-        "message": "Screen mirroring"
+        "message": "Screen/tab casting"
       , "description": "Options page mirroring category name."
     }
   , "optionsMirroringCategoryDescription": {
-        "message": "Screen/Tab mirroring to a Chromecast receiver app."
+        "message": "Mirroring to a Chromecast receiver app."
       , "description": "Options page mirroring category description."
     }
   , "optionsMirroringEnabled": {
-        "message": "Enable screen mirroring (experimental)"
+        "message": "Enable screen/tab casting (experimental)"
       , "description": "Mirroring enabled checkbox label."
     }
   , "optionsMirroringAppId": {
-        "message": "Receiver app ID:"
+        "message": "Mirroring app ID:"
       , "description": "Mirroring app ID input label."
     }
   , "optionsMirroringAppIdDescription": {