Extracting column check constraints

[yuriy-yarosh]

Basic table check constraints extraction.
Naive bracket matching for bracket filtering should do the trick, in most cases.

Closes #471

[kristiandupont]

There are some linter issues. If you fix those, I will merge and publish this. Thank you for contributing!

[yuriy-yarosh]

@kristiandupont done.
It would've been nice to autofix in lint task, as well, e.g.
"lint": "eslint . -f visualstudio --report-unused-disable-directives --fix --ext .js,.ts".

Thank you.