New MongoDB formula, rewritten to use official packages and APT repo

Mostly a rewrite to use the official mongodb packages so we can use 2.6.5.

Also have tidied up and automated (tho still needs work) the admin user creation, and normal user creation.

There are helpers for replica set creation, and reindexing, recovery.

I'm not 100% sure this is a good pattern to follow, if we wish to consider these modules as 'more shareable'. It's creating dependencies that are not strictly required.

I'll discuss offline though, and put these includes in for now.