popovers: Add a clear status option in user popover.

Accomplished by adding a function to clear the status message with
an empty string. The html is then updated to reflect changes without a
refresh.

Currently, it's a small hassle to clear a status message.  This option
makes things a bit easier.

Fixes #11630.

tools/lib/capitalization.py

@@ -126,6 +126,8 @@ IGNORED_PHRASES = [
     r"^new_emoji$",
     # Used to refer custom time limits
     r"\bN\b",
+    # Capital c feels obtrusive in clear status option
+    r"clear",
 
     r"group private messages with __recipient__",
     r"private messages with __recipient__",