Add Zotlabs\Lib\Mailer class to replace z_mail function.

See merge request !2172

(cherry picked from commit c6269854)

Co-authored-by: Saiwal K <sk@utsukta.org>

Fix #1879: Emails with + in local part was rejected.

See merge request !2170

Add PHPStan as a developer dependency.

See merge request !2169

Several issues discovered by PHPStan

See merge request !2168

Fix invocation of DB_Update::run.

See merge request !2167

PHPStan is a static PHP code analyzer that's aimed at finding actual
bugs in the code. Where PHP Code Sniffer is about codeing standards,
PHPStan is about correctness of code.

The provided configuration file (`phpstan.neon.dist`) is configured to
use the _lowest_ level of checks that PHPStan will report on. See
https://phpstan.org/user-guide/rule-levels for information about the
various rule levels.

Run an analysis of the code base like this:

    % ./vendor/bin/phpstan

It will output any found issues to stdout.

You can also run it like this:

    % ./vendor/bin/phpstan --error-format=raw > phpstan.log

This will give you an output file in a format that's suitable for use
with typical editors for mapping errors to source locations.

(cherry picked from commit 8268ed1b)

Co-authored-by: Mario <mario@mariovavti.com>

Thought this should have been part of the change set that turned the
DB_Update routine to a static function instead of a constructor to an
object that is not used.

This reverts commit 2c17d0b0

Begin refactoring Module\Item

See merge request !2166

Remove import of non-existing class in test.

See merge request !2165

This also allows us to deduplicate initialization and validation.

These seem to be entirely independent, so moving the body of the if
statements to separate functions should be fine.