remove deprecated get_logged_in_user_names
default allow_destroy_db to True, as documented

Also, improve error message when set to False

Example configuration had allow_destroy_db: True in it for a long time.
full-documented-m2ee.yaml says the default value for this option is
True, but it's False. Also, allow_destroy_db was dropped from the
user-specific example some time ago, because the value in there was
supposedly the default value, which it's not.

Well, now it is. By default, restoredb and emptydb are enabled. When
needed, they can be explicitely disabled by using allow_destroy_db
False.
Apify unpack

Also, move mxclientsystem symlink handling to unpack.
Move complete_unpack handling to the cli part of m2ee.
Move user input to cli.
Stop on unzip errors.
unpack: more trace logging and error handling

Trace log what command is executed via subprocess and trace log stdout
and stderr output by default.
Improve error message when the unzip program is not found. The 'No such
file or directory' made users think their deployment archive file could
not be found, instead of the unzip program itself.
Apify start/stop

Move all progress logging that is not specific to user-interaction to
the core wrapper methodes.
Make a little start to document admin action return codes.
Apify pgutil... (move cli-specific stuff to cli)
Merge apification Part I (start/stop, unpack, *db)

Merge branch 'apification' into develop