changed how DPW model handles file upload functions for checking and setting upload directory: * moved duplicate code for checking existance of uploaded file into discrete function * initialised '_upload_dir' value as a param during file check function to avoid requierement for duplication in route and model; put rudimentary date check on sqlite3 db (still permits invalid dates); new test files
fixed init_db.sql schema to work with sqlite3 which can only execute single statements per dbh->do() call; changed DB method from D2 plugin to DBIx::Simple; new routes.t for testing all functions
