Copy entry between databases

**Is your feature request related to a problem? Please describe.**
Let's suppose you have 2 different databases and you wanna copy an entry from one to another. Currently, the only way is to create a new entry on the desired db and copy field by field. This has the disadvantage of being very time consuming and also it won't copy the history.

**Describe the solution you'd like**
The ideal solution would be to somehow retain the copied entry when closing the database and opening another one, so the entry can be pasted into there.

**Describe alternatives you've considered**
Maybe a more feasible and secure alternative would be to create an export option as follow: when tapping and holding an entry, add a new export button in the lower tab along with the cut, copy and three dots buttons. When clicking on this export button a new window will be opened so the user can select a destiny database. After selecting the target database and unlocking it, both databases will be unlocked at the same time, allowing the entry to be copied between them. After the exportation, the target database is automatically locked again and the window goes back to where it was. This option could be implemented for folders too.

Thanks in advanced. Much respect for this project 👏👍

Start by examining the existing long-press entry actions, lower action bar, database selection, and database lock/unlock flows described in the issue. The feature is done when an entry, including its history, can be transferred between two databases securely, with the target database locked again afterward; folder support is an optional extension mentioned by the request.

Written by the indexing model from the issue text.