[IMP] web: in `boolean_button`, move options to inner elements to handle translations

In practice, we replace:

    <field name="active" widget="boolean_button"
        options='{"true": "Active", "false": "Inactive"}'/>

by:

    <field name="active" widget="boolean_button">
        <span class="o_stat_text o_true text-success">Active</span>
        <span class="o_stat_text o_false text-danger">Inactive</span>
    </field>