Improve readability and visibility of *nrepl-messages* buffer

Make requests and responses appear differently from each other:

```
(--->
  id	"61"
  op	"load-file"
  session	"c705ea4f-b392-4583-89b5-02d02a7bab1f"
  file	"(ns user)\n\n\n\n\n\n\n\n\n\n\n\n34"
  file-path	"/home/vitoshka/.lein/profiles.clj"
  file-name	"profiles.clj")
(<-
  id	"61"
  ns	"user"
  session	"c705ea4f-b392-4583-89b5-02d02a7bab1f"
  value	"34")
(<-
  id	"61"
  session	"c705ea4f-b392-4583-89b5-02d02a7bab1f"
  status	("done")
)
```



Also  make `*nrepl-messages*` buffer scroll to bottom on new messages when visible.