fix: Do not render hidden form fields twice

[Dosenpfand]

Description

With all existing form widgets hidden fields are rendered twice, once via {{form.hidden_tag()}} and once via {{ lib.render_field(...) }}
This PR excludes the rendering from lib.render_field().
Additionally, it gets rid of a closing </td> for every hidden field for which there was no opening tag.
There is still a empty <tr></tr> remaining, because the code structure.

Example

Before

<form id="model_form" action="" method="post" enctype="multipart/form-data">
<input id="id" name="id" type="hidden" value="6">
<input id="csrf_token" name="csrf_token" type="hidden" value="IjQ5NWM1YmE5MDRmOGYzZGY1OGQwMjIwNGNkMTU4MzZjNDgwYmZiMDUi.Ynq7_A.uwEWVJea7w42o2ZMe83znKaQR4o">
        <div class="table-responsive">
            <table class="table table-bordered">
                        <tr>
            <input id="id" name="id" type="hidden" value="6">
            </td>
                        </tr>
                        <tr>

After

<form id="model_form" action="" method="post" enctype="multipart/form-data">
<input id="id" name="id" type="hidden" value="6">
<input id="csrf_token" name="csrf_token" type="hidden" value="ImQ3MTc5ZDE4ZDYzYTVkZGNkMDZjYjIwNjFiZjQyY2ViNzZhYzcyYzki.YnrQBA.lh6UCFkoGUugpTCwdUbBNq6zlRM">
        <div class="table-responsive">
            <table class="table table-bordered"> 
                        <tr>
                        </tr>

ADDITIONAL INFORMATION

• Has associated issue:
• Is CRUD MVC related.
• Is Auth, RBAC security related.
• Changes the security db schema.
• Introduces new feature
• Removes existing feature

[dpgaspar]

Thank you, once more @Dosenpfand!