Basic placeholder webui

Adds the bare minimum files to have a functional web interface with
placeholder sidebar, home and admin pages.

source/webui/templates/errors/unhandled-exception.tpl

@@ -0,0 +1,46 @@
+<h2>An unhandled error has occurred</h2>
+<p>
+	There was a problem trying to complete the requested action. Please try again and if the problem persists, let us know.
+</p>
+
+{if $display_exceptions}
+<p>
+	An unhandled exception was caught during the page template processing. The full details are shown below:
+</p>
+<table class="exception-details">
+	<colgroup id="header">
+		<col />
+	</colgroup>
+	<colgroup>
+		<col />
+	</colgroup>
+	<tbody>
+		<tr>
+			<th>Exception</th>
+			<td>{$exception_type}</td>
+		</tr>
+		<tr>
+			<th>File</th>
+			<td>{$exception->getFile()}</td>
+		</tr>
+		<tr>
+			<th>Line</th>
+			<td>{$exception->getLine()}</td>
+		</tr>
+		<tr>
+			<th>Message</th>
+			<td>{$exception->getMessage()}</td>
+		</tr>
+		<tr>
+			<th>Stack Trace</th>
+			<td><pre>{$exception->getTrace()|print_r}</pre></td>
+		</tr>
+	</tbody>
+</table>
+
+<p>
+	<em>Note:</em> Exception details should not be displayed on production systems.
+	Disable the <a href="{$base_uri}admin/settings/key/debug.show_exceptions/"><code>debug.show_exceptions</code></a>
+	setting to omit the exception details from this page.
+</p>
+{/if}