Add user name and host name to user-specific file directory

[JoleneSun111]

Fixes #572, user-specific file directory should show user name. Implement a hover on user-specific file directory. If the mouse is on hower, JabRef displays: user: {username}, host: {hostname}.

Describe the changes you have made here: Change the src/main/java/org/jabref/gui/libraryproperties/general, add two properties to display the username and hostname in the frontend. Fixed kopper issue : #572 https://github.com/koppor/jabref/issues/572

Mandatory checks

• [x] Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• [x] Tests created for changes (if applicable)
• [x] Manually tested changed features in running JabRef (always required)
• [x] Screenshots added in PR description (for UI changes)
• [x] Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• [x] Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[calixtus]

There went sthg wrong, when i tried to resolve merge conflicts with in a PR, sorry for that.

[calixtus]

Im afraid you have to create a new PR, but please this time targeting JabRef:JabRef, this repo is just a mirror.

[koppor]

Regrading the screenshot: The tooltip looks good. - The content of the text field seems to have a prefix inside, but maybe just a quirk because of the screenshot.