added sqla tools to gently recreate schema
added support for session params in custom `sesssion_maker`
modifying a copy of `session_params` when setting default `autoflush` value
removed implicit `Sqla` cli import
moving `gentle_drop_tables` as `drop_everything` to `iktomi.cli.sqla`
no more need in `iktomi.cli.sqla_tools`
Merge pull request #101 from riffm/sqla-tools

added sqla tools to gently recreate schema
Merge pull request #102 from riffm/session_maker-update

added support for session params in custom `sesssion_maker`