GUACAMOLE-434: Add parameter value and translation string for UK English keyboard layout.

guacamole-ext/src/main/resources/org/apache/guacamole/protocols/rdp.json

@@ -92,6 +92,7 @@
                     "options" : [
                         "",
                         "de-de-qwertz",
+                        "en-gb-qwerty",
                         "en-us-qwerty",
                         "es-es-qwerty",
                         "failsafe",

guacamole/src/main/webapp/translations/en.json

@@ -386,6 +386,7 @@
 
         "FIELD_OPTION_SERVER_LAYOUT_DE_DE_QWERTZ" : "German (Qwertz)",
         "FIELD_OPTION_SERVER_LAYOUT_EMPTY"        : "",
+        "FIELD_OPTION_SERVER_LAYOUT_EN_GB_QWERTY" : "UK English (Qwerty)",
         "FIELD_OPTION_SERVER_LAYOUT_EN_US_QWERTY" : "US English (Qwerty)",
         "FIELD_OPTION_SERVER_LAYOUT_ES_ES_QWERTY" : "Spanish (Qwerty)",
         "FIELD_OPTION_SERVER_LAYOUT_FAILSAFE"     : "Unicode",