Use declarative bases for the data models

Automapping proved difficult to wrangle many-many relationship naming
and wasn't particularly ergonomic. We may as well just use manual ORM
specifications...

src/pyelephant.py

@@ -1,13 +1,22 @@
 #!/usr/bin/env python3
 
 import sqlalchemy as sa
-import sqlalchemy.ext.automap
+import sqlalchemy.ext.declarative.base
 
 import dateparser
 
 ###############################################################################
-Base = sa.ext.automap.automap_base()
-Task = None
+Base = sqlalchemy.ext.declarative.declarative_base()
+
+
+class Task(Base):
+    __tablename__ = "tasks"
+
+    id = sa.Column(sa.Integer, primary_key=True)
+    title = sa.Column(sa.String, nullable=False)
+    created_at = sa.Column(sa.DateTime, server_default=sa.func.current_timestamp(), nullable=False)
+    due_at = sa.Column(sa.DateTime, nullable=True)
+    active = sa.Column(sa.Boolean, server_default=sa.sql.expression.true(), nullable=False)
 
 
 ###############################################################################
@@ -107,11 +116,6 @@ if __name__ == '__main__':
         dbpath = os.path.realpath(os.path.join(dirname, '..', 'db', 'data.sqlite'))
         db = sa.create_engine(f"sqlite:///{dbpath}")
 
-        Base.prepare(db, reflect=True)
-
-        global Task
-        Task = Base.classes.tasks
-
         session = sa.orm.Session(db)
         args = vars(args)
         func = args['func']