[IMP] website: Add a class btn-multi-line to allow multi line labels on buttons

On website_quote, according to the translation, the label may become much larger than
the button width. By default the bootstrap btn class has the property 'white-space: nowrap'
Here the goal is to add a class which will be used for these kind of cases.

addons/website/static/src/css/website.css

@@ -238,6 +238,10 @@ ul.nav-stacked > li > a {
   width: 220px;
 }
 
+.o_normalwhitespace {
+  white-space: normal;
+}
+
 .oe_demo {
   position: relative;
 }

addons/website/static/src/css/website.sass

@@ -185,6 +185,8 @@ ul.nav-stacked > li > a
 .logo-img
     width: 220px
 
+.o_normalwhitespace
+    white-space: normal
 
 .oe_demo
     position: relative

addons/website_quote/views/website_quotation.xml

@@ -138,7 +138,7 @@
                               <a t-if="order_valid" class="btn btn-primary btn-block" data-toggle="modal" data-target="#modalaccept">
                                   <i class="fa fa-check"></i> Accept Order
                               </a>
-                              <a t-if="not order_valid" href="#discussion" class="btn btn-info btn-block">
+                              <a t-if="not order_valid" href="#discussion" class="btn btn-info btn-block o_normalwhitespace">
                                   <strong>This offer expired!</strong><br/>
                                   Contact us for new quote.
                               </a>