Use block helpers in attributes again in accounts-ui

Now that it's once again supported

packages/accounts-ui-unstyled/login_buttons_dialogs.html

@@ -97,7 +97,7 @@
         </div>
         <a class="accounts-close configure-login-service-dismiss-button">&times;</a>
 
-        <div class="login-button login-button-configure {{additionalClasses}}"
+        <div class="login-button login-button-configure {{#if saveDisabled}}login-button-disabled{{/if}}"
              id="configure-login-service-dialog-save-configuration">
           Save Configuration
         </div>

packages/accounts-ui-unstyled/login_buttons_dialogs.js

@@ -226,11 +226,8 @@ Template._configureLoginServiceDialog.configurationSteps = function () {
   return configureLoginServiceDialogTemplateForService();
 };
 
-Template._configureLoginServiceDialog.additionalClasses = function () {
-  if (loginButtonsSession.get('configureLoginServiceDialogSaveDisabled'))
-    return "login-button-disabled";
-  else
-    return "";
+Template._configureLoginServiceDialog.saveDisabled = function () {
+  return loginButtonsSession.get('configureLoginServiceDialogSaveDisabled');
 };
 
 // XXX from http://epeli.github.com/underscore.string/lib/underscore.string.js

packages/accounts-ui-unstyled/login_buttons_single.html

@@ -1,6 +1,6 @@
 <template name="_loginButtonsLoggedOutSingleLoginButton">
   <div class="login-text-and-button">
-    <div class="login-button single-login-button {{additionalClasses}}"
+    <div class="login-button single-login-button {{#unless configured}}configure-button{{/unless}}"
          id="login-buttons-{{name}}">
       <div class="login-image" id="login-buttons-image-{{name}}"></div>
       {{#if configured}}

packages/accounts-ui-unstyled/login_buttons_single.js

@@ -33,13 +33,6 @@ Template._loginButtonsLoggedOutSingleLoginButton.configured = function () {
   return !!ServiceConfiguration.configurations.findOne({service: this.name});
 };
 
-Template._loginButtonsLoggedOutSingleLoginButton.additionalClasses = function () {
-  if (!!ServiceConfiguration.configurations.findOne({service: this.name}))
-    return "";
-  else
-    return "configure-button";
-};
-
 Template._loginButtonsLoggedOutSingleLoginButton.capitalizedName = function () {
   if (this.name === 'github')
     // XXX we should allow service packages to set their capitalized name