Improve appearence consistency of settings pages (#13938)

* Fix header button changing header size in settings pages

* Make form buttons look more like a part of the form in settings pages

- Put buttons closer, using same distance as between inputs
- Make buton font size a bit smaller to blend a bit more
- Add the class button to button tags for consisent styling

app/views/admin/accounts/index.html.haml

@@ -38,7 +38,7 @@
           = text_field_tag key, params[key], class: 'string optional', placeholder: I18n.t("admin.accounts.#{key}")
 
     .actions
-      %button= t('admin.accounts.search')
+      %button.button= t('admin.accounts.search')
       = link_to t('admin.accounts.reset'), admin_accounts_path, class: 'button negative'
 
 .table-wrapper