[FIX] event: correctly set default hashtag on event coming from category

Wrong event category field was used leading to an incoherent feature.

This commit also improves event form view to add an '#' before the
hashtag field so that users understand they don't have to put it.

addons/event/models/event.py

@@ -239,7 +239,7 @@ class EventEvent(models.Model):
             if self.event_type_id.use_reply_to:
                 self.reply_to = self.event_type_id.default_reply_to
 
-            if self.event_type_id.use_reply_to:
+            if self.event_type_id.use_hashtag:
                 self.twitter_hashtag = self.event_type_id.default_hashtag
 
             if self.event_type_id.use_timezone:

addons/event/views/event_views.xml

@@ -230,7 +230,11 @@
                             <group>
                                 <field name="event_type_id" options="{'no_create':True}"/>
                                 <field name="reply_to" string="Contact Email"/>
-                                <field name="twitter_hashtag"/>
+                                <label for="twitter_hashtag"/>
+                                <div>
+                                    <span class="oe_inline"># </span>
+                                    <field name="twitter_hashtag" nolabel="1" class="oe_inline"/>
+                                </div>
                                 <field name="auto_confirm" groups="base.group_no_one"/>
                             </group>
                             <group>