Port to Python3, use up to date SQLAlchemy, plus some extensions

[AlainLich]

Hi, This PR:

1. ports to Python3, but not compatible with Python2 (sorry). Some areas not covered (geoIP, ̀logfilter`).
2. database interfaces supported: Mysql 8.x and SQLite. This required moving to up to date SQLAlchemy, getting rid of sqlsoup
3. some extensions, as described on https://github.com/AlainLich/logtools/blob/ALPython3/PYTHON3-ADDITIONS.md. This allows for more log formats, added flexibility, handling of JSON input.
4. tests see https://github.com/AlainLich/logtools/actions (including Mysql and SQLite) Involves some secrets (as defined by Github)

Full functionality depends on using a non standard version of dpath_python https://github.com/AlainLich/dpath-python, for which a PR is pending. May make distribution more complicated.

I will take remarks into account if this facilitates integration, response could depend on amount of work involved.

This is not modular (sorry), things got interesting enough to warrant a PR quite late in the development, when I found out that I had to move to up to date SQLAlchemy, not compatible with sqlsoup.