Add `registration/login.html` to `main/templates/registration/`

[AdrianDAlessandro]

Corresponds to the the GET request component of LoginView.

Reference as {% url 'login' %} in the main index template.

The POST request redirects to the LOGIN_REDIRECT_URL settings variable, which defaults to '/accounts/profile/'. This url is not defined, so we should also change that setting variable to be where we want it to redirect to. I suggest adding the following to rse_competencies_toolkit/settings/settings.py

LOGIN_REDIRECT_URL = "/"

The Django docs provide a sample template, which I have included here:

{% extends "base.html" %}

{% block content %}

{% if form.errors %}
<p>Your username and password didn't match. Please try again.</p>
{% endif %}

{% if next %}
    {% if user.is_authenticated %}
    <p>Your account doesn't have access to this page. To proceed,
    please login with an account that has access.</p>
    {% else %}
    <p>Please login to see this page.</p>
    {% endif %}
{% endif %}

<form method="post" action="{% url 'login' %}">
{% csrf_token %}
<table>
<tr>
    <td>{{ form.username.label_tag }}</td>
    <td>{{ form.username }}</td>
</tr>
<tr>
    <td>{{ form.password.label_tag }}</td>
    <td>{{ form.password }}</td>
</tr>
</table>

<input type="submit" value="login">
<input type="hidden" name="next" value="{{ next }}">
</form>

{# Assumes you set up the password_reset view in your URLconf #}
<p><a href="{% url 'password_reset' %}">Lost password?</a></p>

{% endblock content %}