Initial checkin of PostgreSQL prototype

The postgres prototype is up and running on webdev-kl2.  This iteration does not include support for redis caching or anything, but it's very fast anyways.

add_mapping_file.py is used to upload mapping files to the database. Features:
- Automatically (naively) determines column data type
- pass ```-d``` to drop tables and clear data for the study before adding

query_qiime_md.py provides a basic query interface. Features:
- select all samples that have a particular metadata trait, e.g., ```python query_qiime_md.py 'sulfide>0.007'```
- If multiple tables are hit with the query (this is likely), pass ```-c``` to select only columns that are common to all tables hit. By default, all data for each sample is returned

I have not yet implemented the ability to select common columns AND some non-common columns.  You also cannot yet do queries with multiple parameters (mostly because I didn't want to spend time right now on parsing multi-part queries, e.g., ```python query_qiime_md.py 'sulfide>0.007&&sulfate>0.1'```