Transaction API for DB Transactions

See merge request !406

.. before we start adding the transactional tests (and testing the
rollback).

Use Async.race in serverCLI start-all to fix initialisation bug

See merge request !404

It's a simple DB query, it shouldn't need any extra effect.

This commit uses the `race` function from the async library to fix a bug
where exceptions raised from the server async wouldn't be caught by the
top-level code.

The bug was stemming from the fact that `runAllWorkers` is **blocking**,
despite its usage of `forConcurrently_`. Therefore we were never
actually running the `wait` function below, but rather we were hanging
waiting on the result of the first function.

As a result the server could die but the workers could keep the main
thread alive, causing the bug we just saw as part of #463.

Proper incremental TSV parser

See merge request !402

README: add info about system postgresql configuration

See merge request !403

This commit introduces/improves the `parseTvsWithDiagnostics`
function to parse the input TSV incrementally, collecting errors
as we go, and eventually reporting them upstream via the newly
added `emitTsvParseWarning` function.

This will pave the way for a more thorough refactoring to
be able to emit diagnostics after parsing.

Resolve "Import/export in SQLite format"

See merge request !393

Also, no need for `liftBase` in `getCorpusSQLite`.

Resolve "Implement temporary file storage"

See merge request !392

In an attempt to make the TSV parser more lenient for the absence of the
forms column, I have used NoHeader in the `decodeWithP` call, but that
caused the first line of the TSVs with a header to be interpreted as
terms, which is not what we want.