GUACAMOLE-742: Use "data-disabled" instead of "disabled" for directive attributes.

Internet Explorer 11 interprets the "disabled" attribute on all HTML
elements, even unknown elements like AngularJS directives, disabling any
input fields that end up on the DOM tree within those elements. This
breaks the login form.

The alternative "data-disabled" attribute form supported by AngularJS
allows things to work without interference.

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

@@ -9,7 +9,7 @@
         <div class="fields">
             <guac-form-field ng-repeat="field in form.fields" namespace="namespace"
                              ng-if="isVisible(field)"
-                             disabled="disabled"
+                             data-disabled="disabled"
                              field="field" model="values[field.name]"></guac-form-field>
         </div>
 

guacamole/src/main/webapp/app/login/templates/login.html

@@ -27,7 +27,7 @@
                         namespace="'LOGIN'"
                         content="remainingFields"
                         model="enteredValues"
-                        disabled="submitted"></guac-form>
+                        data-disabled="submitted"></guac-form>
                 </div>
 
                 <!-- Login/continue button -->