Fix a couple of issues with telegrams (beeps and HTML tags)

I noticed that beep chars (ASCII 7), which come in some
telegrams (e.g. SBBSecho notices) were being printed as a box
glyph in the web UI. Strip those before emitting the telegram event.

I also noticed that some text was missing from some telegrams
(e.g. <user@addr> portion of email notices) - this was because
the <> chars weren't be html-entity-encoded. So now I'm using
html_encode() to HTML-entity encode the string (not the
white-space) and stripping the Ctrl-A codes here.

It would be kind of cool if the colors in the telegrams could
be retained/displayed, but html_encode sets the background of
the text to black, which doesn't look so hot with the current
theme and stuff. We might want to revisit that (e.g. not strip the
Ctrl-A chars here but rather let html_encode() tranlsate them to
HTML color sequences).

Another thing I noticed, if a telegram doesn't end in a CRLF, the
web UI doesn't automatically add/display a <br>. It probably should
(just in case). All telegrams should end in a CRLF, but you never
know.

web/lib/events/telegram.js

@@ -6,7 +6,13 @@ function cycle() {
     if (time() - last_run <= frequency) return;
     last_run = time();
     const tg = system.get_telegram(user.number);
-    if (tg !== null) emit({ event: 'telegram', data: JSON.stringify(tg) });
+    if (tg !== null) emit({ event: 'telegram'
+		, data: JSON.stringify(html_encode(tg.replace('\7', '').replace(/\1./g, '')
+			, /* ex-ascii */true
+			, /* white-space */false
+			, /* ansi */false
+			, /* ctrl_a */false))
+		});
 }
 
 this;