Add SqliteDBStreamer, converters, and tests

This is in reference to the following issue: https://github.com/columbia-applied-data-science/rosetta/issues/21

I wrote a class called SqliteDBStreamer which is intended to mirror the usage of TextFileStreamer except instead of having a folder of text files as the main source of data, the files are kept in a sqlite3 database which makes many standard file operations much faster.

I personally think this is NOT READY to merge. Each time I look at it, I find little weird things left-over from how I was using the code a month ago (when I basically just hacked it together). But I wanted to throw it up here in case you guys see something really bazaar. I tried to make it as much like TextFileStreamer as possible. In the info_stream, for example, I do not currently have fields like "modification_date". I could add that as a trigger to the sqlitedb file, but I wasn't sure how necessary it was. I also have a few tweaks I need to add that speed this up, but those are minor details aside from the overall setup.

At this point, I'm basically only treating the sqlitedb as a never-changing object (i.e. add files once and then leave them there). Now this probably doesn't make sense (though I've personally not yet had any other use case), but I'm still thinking the best way to deal with those problems. In it's current state basically all sqlite details are hidden, which is pretty nice at the moment.

Anyway I imagine myself making many changes to this, but I figured I might as well throw this up here so you guys can give me some feedback if I'm doing something really stupid. Also I have an analysis that I'm doing for declass which could be used as a guide for using these classes, but I need to adapt it to this newer code (though on the surface it looks basically identical to how it's done with TextFileStreamer). Once I do that it could be good documentation.