improve search query, cleanup directory name

reddit supports a "site:" options which will restrict search
results to a specified domain (i.e. site:imgur.com). I have setup
the code so that we can easily add more domains (like i.minus.com),
so that domains are joined by " OR ".

example search query after we support more domains:
"hey reddit check out my dog (site:imgur.com OR site:i.minus.com)

directory names have been cleaned up a bit before saving images.
I ran into the problem of searching for a string like:
"check out my dog/cat" and the script created a directoy AND a
subdirectory. this change prevents that.