title: How to add monetary symbol in tree view?
body: <p>I want to add monetary symbol in the field amount, it should be like that: $ 8,90 but the symbol doesn't appear. Here is my code:</p>
  
  <pre><code>&lt;page string="Ventes et entrées"&gt;
                      &lt;field name="sale_cash_in_ids"&gt;
                          &lt;tree&gt;
                              &lt;field name="date"/&gt;
                              &lt;field name="name"/&gt;
                              &lt;field name="partner_id"/&gt;
                              &lt;field name="currency_id" groups="base.group_multi_currency"/&gt;
                              &lt;field name="amount" widget="monetary" options="{'currency_field': 'currency_id'}"/&gt;
                          &lt;/tree&gt;
                      &lt;/field&gt;
                      &lt;group class="oe_subtotal_footer oe_right"&gt;
                          &lt;field name="sale_cash_in_sum"/&gt;
                      &lt;/group&gt;
                  &lt;/page&gt;
  </code></pre>
  
  <p>And the python code in pos_session.py:</p>
  
  <pre><code>class AccountBankStatement(models.Model):
  _inherit = "pos.session"
  
  sale_cash_in_ids = fields.One2many(comodel_name="account.bank.statement.line", inverse_name="sale_cash_in_id",
                                     compute="_compute_cash")
  cash_out_ids = fields.One2many(comodel_name="account.bank.statement.line", inverse_name="cash_out_id",
                                 compute="_compute_cash")
  sale_cash_in_sum = fields.Monetary(string="Total", compute="_compute_total")
  cash_out_sum = fields.Monetary(string="Total", compute="_compute_total")
  sale_cash = fields.Monetary(string="Vente", compute="_compute_sum")
  cash_in = fields.Monetary(string="Entrées", compute="_compute_cash_in")
  cash_out = fields.Monetary(string="Dépenses", related="cash_out_sum")*
  </code></pre>
  
  <p>The python code in account_bank_statement.py</p>
  
  <pre><code>class AccountBankStatementLine(models.Model):
  _inherit = 'account.bank.statement.line'
  
  sale_cash_in_id = fields.Many2one(comodel_name="pos.session")
  cash_out_id = fields.Many2one(comodel_name="pos.session")
  </code></pre>