Add support for AutoOpen / child database

[fcrozat]

KeePassXC and Keepass supports automatically opening child database using AutoOpen group ( https://keepassxc.org/docs/KeePassXC_UserGuide.html#_automatic_database_opening / https://keepass.info/plugins.html#keeautoexec ).

This feature, if the application supports opening and searching several databases in memory, allows to share credentials between several people easily (without the hassle of KeeShare https://github.com/hicknhack-software/KeeShare which seems a bit less supported in Keepass* ecosystem).

[gabeweb]

I agree with the support of this feature. In KeePassXC it's very helpful and it should also be so in KeePassDX (especially because of the limitations of a mobile interface).

[J-Jamet]

Linked to #549, depends on the simultaneous opening of databases #209