API: first draft

**First draft of the API** for the tw_harvester

## Things to check
- In the recent versions, Mongoose deprecated execFind();. I replaced it with a simple exec() and it seems ok.
- We have an API for these things: all the data (a bunch of tweets! That crashed my JSONView Chrome module), username selective search.

## TODO
- An API for all the tweets with attached pics.

_Daje_ :)