Support for different DBs

[f-marino]

Adding support for different DB types (eg. MS SQL).

[romainbou]

Note that in #12 I removed datasets in the docker image for Oracle and MS SQL. This was to reduce the size of our Postgres distribution.
This can easily be reverted by removing this line:

geco-i2b2-data-source/build/package/i2b2/download-i2b2-sources.sh

Line 16 in cffc36a

find . -type d -name "sqlserver" -o -name "oracle" -print0 | xargs -0 rm -v -rf "{}"