add alias for booth

Booth can be replaced with any alias by replacing it in alias.en.yml. This change is introduced as some events do not use booth but uses other words such as stand.

app/views/booths/_form.html.haml

@@ -13,15 +13,15 @@
         = f.input :website_url
         = responsibles_selector_input f
         = f.input :invite_responsible,
-          hint: 'This field is to invite unregistered users using their email to become booth responsibles.'
+          hint: "This field is to invite unregistered users using their email to become #{(t'booth_responsible').pluralize}."
         = image_tag f.object.picture.thumb.url if f.object.picture?
         = f.input :picture
 
         %p.text-right
           - if @booth.new_record?
-            = f.submit 'Create Booth Request', class: 'btn btn-success'
+            = f.submit "Create #{(t'booth').capitalize } Request", class: 'btn btn-success'
           - else
-            = f.submit 'Update Booth Request', class: 'btn btn-success'
+            = f.submit "Update #{(t'booth').capitalize } Request", class: 'btn btn-success'
 
   :javascript
     $(document).ready(function() {