Add comment undeletion functionality

Only Developers and Trusted Users can undelete comments.

Signed-off-by: Marcel Korpel <marcel.korpel@gmail.com>
Signed-off-by: Lukas Fleischer <lfleischer@archlinux.org>

web/html/images/action-undo.min.svg

@@ -0,0 +1,3 @@
+<svg xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://www.w3.org/2000/svg" height="8" width="8" version="1.1" xmlns:cc="http://creativecommons.org/ns#" xmlns:dc="http://purl.org/dc/elements/1.1/" viewBox="0 0 8 8">
+<path d="m4.5 0c-1.93 0-3.5 1.57-3.5 3.5v0.5h-1l2 2 2-2h-1v-0.5c0-1.38 1.12-2.5 2.5-2.5s2.5 1.12 2.5 2.5c0-1.93-1.57-3.5-3.5-3.5z" transform="translate(0 1)" fill="#36a"/>
+</svg>

web/html/images/action-undo.svg

@@ -0,0 +1,32 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg
+   xmlns:dc="http://purl.org/dc/elements/1.1/"
+   xmlns:cc="http://creativecommons.org/ns#"
+   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
+   xmlns:svg="http://www.w3.org/2000/svg"
+   xmlns="http://www.w3.org/2000/svg"
+   version="1.1"
+   id="svg2"
+   viewBox="0 0 8 8"
+   height="8"
+   width="8">
+  <metadata
+     id="metadata10">
+    <rdf:RDF>
+      <cc:Work
+         rdf:about="">
+        <dc:format>image/svg+xml</dc:format>
+        <dc:type
+           rdf:resource="http://purl.org/dc/dcmitype/StillImage" />
+        <dc:title></dc:title>
+      </cc:Work>
+    </rdf:RDF>
+  </metadata>
+  <defs
+     id="defs8" />
+  <path
+     style="fill:#3366aa;fill-opacity:1"
+     id="path4"
+     transform="translate(0 1)"
+     d="M4.5 0c-1.93 0-3.5 1.57-3.5 3.5v.5h-1l2 2 2-2h-1v-.5c0-1.38 1.12-2.5 2.5-2.5s2.5 1.12 2.5 2.5c0-1.93-1.57-3.5-3.5-3.5z" />
+</svg>