[FIX] website: remove domain on website demo data

Remove demo data for domain to make it usable on runbot.
Before this commit, when you switch on runbot to website 2, you was redirected
to 0.0.0.0.

+ add tooltip (fgi request)

addons/website/data/website_data.xml

@@ -3,7 +3,7 @@
     <data noupdate="1">
         <record id="default_website" model="website">
             <field name="name">My Website</field>
-            <field name="domain">localhost</field>
+            <field name="domain"></field>
             <field name="company_id" ref="base.main_company"/>
             <field name="user_id" ref="base.public_user"/>
             <field name="favicon" type="base64" file="web/static/src/img/favicon.ico"/>

addons/website/data/website_demo.xml

@@ -3,7 +3,7 @@
     <data noupdate="1">
         <record id="website2" model="website">
             <field name="name">My Website 2</field>
-            <field name="domain">0.0.0.0</field>
+            <field name="domain"></field>
         </record>
 
         <record id="menu_contactus2" model="website.menu">

addons/website/views/res_config_settings_views.xml

@@ -90,7 +90,7 @@
                                         Display this website when users visit this domain
                                     </div>
                                     <div class="mt8">
-                                        <field name="website_domain"/>
+                                        <field name="website_domain" placeholder="www.odoo.com"/>
                                     </div>
                                     <div class="mt8 text-muted" title="You can have 2 websites with same domain AND a condition on country group to select wich website use.">
                                         Once the selection of available websites by domain is done, you can filter by country group.