Captcha and design works.

Added captcha generation. As we're working without JS - there is no
possibility to reload image, only if user will reload whole web page.

Some design works - set monospace font for paste textarea (will
use system-defined default monospace font) and lowered font size
in paste views.

assets/css/style.css

@@ -1,3 +1,9 @@
 #paste-contents {
+    font-family: monospace;
+    font-size: 0.9rem;
     height: 90vh;
+}
+
+.paste-data {
+    font-size: 0.9rem;
 }

assets/index.html

@@ -82,6 +82,16 @@
                             </div>
                         </div>
                     </div>
+                    <div class="field">
+                        <label for="paste-captcha">Captcha:</label>
+                        <div class="control">
+                            <p>
+                                <img id=image src="/captcha/{captchaString}.png" alt="Captcha image">
+                            </p>
+                            <input class="input" type="text" placeholder="Captcha solution" name="paste-captcha-solution" id="paste-captcha-solution">
+                            <input class="input is-hidden" type="text" name="paste-captcha-id" id="paste-captcha-id" readonly value="{captchaString}">
+                        </div>
+                    </div>
                     <div class="field">
                         <div class="control">
                             <input class="button is-success" type="submit" value="Paste!">

assets/paste.html

@@ -32,7 +32,7 @@
             </div>
         </div>
     </nav>
-    <section class="section">
+    <section class="section paste-data">
         {pastedata}
     </section>
 </body>