Fix postgres issue when updating

[nickvergessen]

Postgres could not be used in 12. It installed the tables with wrong names
so we need to ignore it on the update steps. The wrong tables will be
dropped and new tables will be created with further migrations.
But we shouldn't try to migrate data from the old and broken layout.

Fix #578
Fix #543

[enoch85]

So this means that old DB enteries will be purged? I'd like an as clean DB as possible.

[nickvergessen]

Actually its a bit different:

Actually it's not postgres having the problem, but migrations.
Postgres allows camelCased columns, but they need to be quoted.
They were quoted from the old database.xml file but this does
not work anymore in migrations. But that means it worked on
postgres in the past, it just didn't work in 2.9~ to install
since migrations where merged. So we are reverting the check
for postgres and only allow updating from 2.0.0 or later.

This makes sure that when newly installing the migration code
is not run.

Make sure Postgres uses lowercase for the migration generated columns

The issue is that migrations always generate lowercase columns only.
So all columns that were created with database.xml are okay and cC.
But all intermediate columns the migrations create need to be
referenced as lowercase columns in the queries.

In the future we won't have this problem anymore because we switched
to under_score column names for 3.0

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@enoch85 I have no idea what you are talking about

So this means that old DB enteries will be purged?

[Ivansss]

Tested and works 👍

[enoch85]

Nvm, I'm glad it wasn't a PostgreSQL issue.