View/edit browser config in a special browser page

Add the ability to view/edit the browser's config settings via a special
browser page.

It's very simplistic for now, but a good starting point.

Future possibilities:
* Matching config types to html input types
  * colors = html colorpicker
  * options with valid_values = select/multi-select
  * plain text fallbacks where appropriate
  * multi-line text edits for long options (i.e. host-block-lists)

* Javascript option verification
  * switch from submitting changes onblur to onchange if an option passes basic
    verification, etc.

qutebrowser/config/config.py

@@ -520,6 +520,13 @@ class ConfigManager(QObject):
             if self._initialized:
                 self._after_set(sectname, optname)
 
+    @pyqtSlot(str, str, str)
+    def set_javascript(self, sectname, optname, value):
+        try:
+            self.set('conf', sectname, optname, value)
+        except configtypes.ValidationError as e:
+            message.error(e)
+
     @cmdutils.register(instance='config')
     def save(self):
         """Save the config file."""

qutebrowser/html/settings.html

@@ -0,0 +1,37 @@
+{% extends "base.html" %}
+
+{% block script %}
+var cset = function(section, option, el) {
+  value = el.value;
+  window.qutesettings.set_javascript(section, option, value);
+}
+{% endblock %}
+
+{% block style %}
+table { border: 1px solid grey; border-collapse: collapse; }
+pre { margin: 2px; }
+th, td { border: 1px solid grey; padding: 0px 5px; }
+th { background: lightgrey; }
+th pre { color: grey; text-align: left; }
+{% endblock %}
+
+{% block content %}
+<header><h1>{{ title }}</h1></header>
+<table>
+{% for section in config.DATA %}
+  <tr><th colspan="2"><h3>{{ section }}</h3><pre>{{ config.SECTION_DESC.get(section)|wordwrap(width=120) }}</pre></th></tr>
+  {% for d, e in config.DATA.get(section).items() %}
+    <tr>
+      <td>{{ d }} (Current: {{ e.value()|truncate(100) }})</td>
+      <td>
+        <input type="input"
+          onblur="cset('{{ section }}', '{{ d }}', this)"
+          value="{{ e.value() }}">
+        </input>
+      </td>
+    </tr>
+  {% endfor %}
+{% endfor %}
+</table>
+
+{% endblock %}

qutebrowser/network/qutescheme.py

@@ -31,7 +31,8 @@ from PyQt5.QtNetwork import QNetworkReply
 
 import qutebrowser
 from qutebrowser.network import schemehandler, networkreply
-from qutebrowser.utils import version, utils, jinja, log, message, docutils
+from qutebrowser.utils import (version, utils, jinja, log, message, docutils,
+                               objreg)
 
 
 pyeval_output = ":pyeval was never called"
@@ -146,6 +147,19 @@ def qute_help(win_id, request):
     return utils.read_file(path).encode('UTF-8', errors='xmlcharrefreplace')
 
 
+def qute_settings(win_id, request):
+    """Handler for qute:settings. View/change qute configuration"""
+    from qutebrowser.config import configdata
+
+    cfg = objreg.get('config')
+    frame = objreg.get('webview', scope='tab').page().mainFrame()
+    frame.addToJavaScriptWindowObject("qutesettings", cfg)
+
+    html = jinja.env.get_template('settings.html').render(
+        title='settings', config=configdata, cfg=cfg)
+    return html.encode('UTF-8', errors='xmlcharrefreplace')
+
+
 HANDLERS = {
     'pyeval': qute_pyeval,
     'version': qute_version,
@@ -153,4 +167,5 @@ HANDLERS = {
     'log': qute_log,
     'gpl': qute_gpl,
     'help': qute_help,
+    'settings': qute_settings,
 }