Added search by ObjectID and Set up a distinct cookie key name.

Swapped out the "Number" checkbox for a select that still allows to search as number, but also adds the option to search as an ObjectID.  Validation and conversion are done in bson.js to allow for reuse.  This addresses issue #20 and allows  search using ObjectID("xxxx"), "xxxx" or xxxx by stripping any of them down to just xxxx.  It also requires 24 hex digits and lets the user know if not enough were passed in any of the formats.

Also, because this application is likely to be used as a tool for developing other express applications, I've set up the default cookie to be mongo-express to keep it from overwriting express cookies by default.  I set up a cookieKeyName attribute in config.js to make it harder to miss when getting set up.