GUAC-1213: Add date/time field format placeholders.

guacamole/src/main/webapp/app/form/templates/dateField.html

@@ -2,6 +2,7 @@
     <input type="date"
            ng-model="typedValue"
            ng-model-options="modelOptions"
+           placeholder="{{'FORM.FIELD_PLACEHOLDER_DATE' | translate}}"
            autocorrect="off"
            autocapitalize="off"/>
 </div>

guacamole/src/main/webapp/app/form/templates/timeField.html

@@ -2,6 +2,7 @@
     <input type="time"
            ng-model="typedValue"
            ng-model-options="modelOptions"
+           placeholder="{{'FORM.FIELD_PLACEHOLDER_TIME' | translate}}"
            autocorrect="off"
            autocapitalize="off"/>
 </div>

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

@@ -127,6 +127,9 @@
 
     "FORM" : {
 
+        "FIELD_PLACEHOLDER_DATE" : "YYYY-MM-DD",
+        "FIELD_PLACEHOLDER_TIME" : "HH:MM:SS",
+
         "HELP_SHOW_PASSWORD" : "Click to show password",
         "HELP_HIDE_PASSWORD" : "Click to hide password"