Extend Rails log admin viewer to specify lines not containing a string

[philayres]

In the admin Rail Log viewer, a field currently allows for a grep of a matching Regex, followed by a certain number of lines for additional context.

We want to add another field that limits the matched lines to those not matching a certain string (or Regex). This must not filter the following context lines though.

[philayres]

Also, include some links to common searches