DeepDive enjoys destroying input database and tables

[alldefector]

Almost always the input data comes from existing tables in a DB. But DD would happily destroy the database specified in db.url and/or the input tables without asking...

What we end up doing is to always run this sequence of commands to keep the input data safe:

deepdive mark todo process/init/app
deepdive mark done process/init/app
deepdive mark done data/input_table
deepdive do all

I think we should remove the "drop db" attempt no matter what. For "drop table", it should be invoked only when the relation is marked as, say, "external".

[alldefector]

This removes dropdb: https://github.com/HazyResearch/deepdive/pull/592/commits/90a371bb423c2b5c68bd0a6015c57da60e15c2a4