[FIX] mail, web: use 'o_input' class on kanban and discuss elements

Since the new views, the 'o_input' class has to be set explicitely on
<input/>, <select/> and <textarea/> elements to have the proper styling.

addons/mail/static/src/xml/client_action.xml

@@ -84,7 +84,7 @@
     <t t-name="mail.chat.SidebarItems">
         <div t-if="!disable_add_channel" class="o_mail_add_channel" t-attf-data-type="#{channel_type}">
             <span t-if="display_hash">#</span>
-            <input type="text" t-attf-placeholder="#{input_placeholder}"/>
+            <input type="text" class="o_input" t-attf-placeholder="#{input_placeholder}"/>
         </div>
         <t t-foreach="channels" t-as="channel">
             <t t-set="counter" t-value="channel.is_chat ? channel.unread_counter : channel.needaction_counter"/>
@@ -134,6 +134,6 @@
 
     <!-- Invite dialog's content -->
     <div t-name="mail.PartnerInviteDialog">
-        <input type="text" class="o_mail_chat_partner_invite_input" id="mail_search_partners"/>
+        <input type="text" class="o_input o_mail_chat_partner_invite_input" id="mail_search_partners"/>
     </div>
 </templates>

addons/mail/static/src/xml/composer.xml

@@ -5,7 +5,7 @@
          <div class="o_composer_attachments_list"/>
          <t t-if="widget.extended">
              <div class="o_composer_subject">
-                 <input tabindex="1" type="text" placeholder="Subject"></input>
+                 <input tabindex="1" type="text" class="o_input" placeholder="Subject"></input>
                  <div class="btn-group o_composer_buttons">
                     <button tabindex="3" class="btn btn-sm btn-primary o_composer_button_send" type="button"><t t-esc="widget.options.send_text"/></button>
                     <button tabindex="4" class="btn btn-sm btn-icon fa fa-smile-o o_composer_button_emoji" type="button" data-toggle="popover"/>
@@ -15,7 +15,7 @@
          </t>
          <div t-attf-class="o_composer #{widget.extended ? 'o_extended_composer' : ''}">
              <div class="o_composer_input">
-                 <textarea class="o_composer_text_field" tabindex="2" placeholder="Write something..."/>
+                 <textarea class="o_input o_composer_text_field" tabindex="2" placeholder="Write something..."/>
              </div>
              <t t-if="!widget.extended">
                  <div class="btn-group o_composer_buttons">

addons/web/static/src/xml/kanban.xml

@@ -48,7 +48,7 @@
             <span class="o_kanban_title">Add new Column</span>
         </div>
         <div class="o_kanban_quick_create">
-            <input type="text" placeholder="Add"/>
+            <input type="text" class="o_input" placeholder="Add"/>
             <button class="btn btn-sm btn-primary o_kanban_add">Add</button>
             <button class="btn btn-sm btn-default o_kanban_cancel">Discard</button>
         </div>
@@ -57,7 +57,7 @@
 
 <t t-name="KanbanView.QuickCreate">
     <div class="o_kanban_quick_create">
-        <input type="text" placeholder="Add"/>
+        <input type="text" class="o_input" placeholder="Add"/>
         <button class="btn btn-sm btn-primary o_kanban_add">Add</button>
         <button class="btn btn-sm btn-default o_kanban_cancel">Discard</button>
     </div>