Use knexjs instead of raw queries

[knownasilya]

Seems like the queries are pretty standard, which would make them an ideal candidate for knexjs. Knex supports the same databases, which would cut your code base down so there is less to manage.

[simov]

Thanks @knownasilya I'll take a look at it!

[simov]

I ended up rolling my own query builder instead. Also I moved all query generation related code to one common place https://github.com/simov/express-admin/tree/master/lib/qb

[knownasilya]

@simov nice!