This commit adds support for tracing
audit log events.

Therefore, this commit removes the global
HTTP write timeout. The problem with server-wide
timeouts is that as a HTTP handler you cannot
adjust/opt-out of the timeout. This makes it
impossible to implement long-running server tasks
like tracing logs.

Instead, this commit implements a custom timeout
handler - similar to https://golang.org/pkg/net/http#TimeoutHandler
The custom timeout handler and Go's TimeoutHandler
differ in implementation details. See documentation.

Now, each HTTP handler that requires a (write) timeout
must be wrapped by a timeout handler. The server-wide
write-timeout is explicitly set to 0.

Further, this commit implements a audit log tracing CLI
that prints a human-readable text output to a TTY and JSON
otherwise.