Add psalm to integration

Add psalm as a dev dependency and solve some issues that psalm had with the existing code. Also, when analyzing a code base with psalm we now give more detailed information about the expected arrays in DBInterface.

v0.7: Add docker tests & rework interfaces

- Major refactoring, changing the interfaces. Not backwards
  compatible, especially upsert was converted to insertOrUpdate
- Add docker tests with real databases, and adjust some aspects
  accordingly
- Introduce LargeObject for Postgres handling
- Update documentation

v0.6.5: Better confirmation for delete all and update all

We made it more consistent and also added the check to
the update query builder, as updating all entries is
just as dangerous as deleting them all.

v0.6.4: Must confirm delete all in query builder

With the query builder it is easy to delete all entries in a
table by forgetting the "where" restriction - now there is
a mandatory confirmDeleteAll call if no where restriction is
defined, to make deleting all entries explicit.

v0.6.3: Small fixes & improvements

- Extract SelectIteratorTrait from SelectIterator
- Check flattenFields more thoroughly, and remove it in some
  parts where it is not allowed anymore
- Improve documentation with more examples

v0.6.2: Add IteratorAggregate usage for SelectEntries

Makes it possible to leave out the explicit getIterator call
when using SelectEntries.

Slight fix to DBDebug

DBDebug tripped over functions in the debug stack, like array_map. These are now skipped, only classes are recognized in the stack trace.

Restrict flattenFields

The previous implementation was not really consistent - now we only allow it for fetchAll, which makes much more sense.

Add query builder

Add DBBuilderInterface with implementation

- Possibility to more easily create structured queries
- Add tests covering all options
- Add more strict ruleset.xml for phpcs
- Adjust documentation

Better documentation

v0.5.5

Improve documentation