PATCH: Dialogue control buttons should be consistent (pgAdmin4)

Hi,

PFA patch to fix the issue where some dialogue control buttons were not
consistent with others dialogs.
RM#1364

Patch fixes,
1) Preferences: Close, Maximise, Pin
- Removed Pin button

2) Wizards: Close
- Added Maximise button, which is can used with 'show_header_maximize_btn'
option.

3) Properties: Close
- N/A, As this is custom wcDocker panel not alertify dialog.

4) User manager: Maximise
- We can't have close button in User Manager as data validation was main
requirement, If user clicks on right top close button while having dirty
data in dialog then we can't stop alertify dialog from closing even with
confirm prompt hence we have removed the button.

--
Regards,
Murtuza Zabuawala
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company