Migrate app to use WTForms for auth form validation

- Not finished yet, major styling breakage in this commit
- Also encapsulated GET & POST requests of /login and /signup routes into one route.

templates/pages/auth/login.html

@@ -1,4 +1,6 @@
 {% extends 'layouts/index.html' %}
+{% from 'macros.html' import render_field %}
+
 {% block content %}
     {% with messages = get_flashed_messages() %}
         {% if messages %}
@@ -7,29 +9,14 @@
             </span>
         {% endif %}
     {% endwith %}
-    <form method="POST" action="{{ url_for('auth.login_post') }}" class="login-form">
-        <div class="field">
-            <div class="control">
-                Username
-                <input class="input is-large" type="text" name="username" placeholder="Username" autofocus="true">
-            </div>
-        </div>
+    <form method="POST" action="{{ url_for('auth.login') }}" class="login-form">
+        {{ render_field(form.username) }}
+        {{ render_field(form.password) }}
+        {{ render_field(form.remember_me) }}
+            <p><input type=submit value=Login>
 
-        <div class="field">
-            <div class="control">
-                Password
-                <input class="input is-large" type="password" name="password" placeholder="Password">
-            </div>
-        </div>
-        <div class="field">
-            <label class="checkbox">
-                <input type="checkbox">
-                Remember me
-            </label>
-        </div>
-        <button class="button">Login</button>
     </form>
     <p class="form-subtext">
-        Don't have a login? <a href="{{ url_for('main.signup') }}">Sign-up</a> instead!
+        Don't have a login? <a href="{{ url_for('auth.signup') }}">Sign-up</a> instead!
     </p>
 {% endblock content %}