Remove password from memory after login

[dominikl]

Some improvements how password is handled in the gateway (from https://forum.image.sc/t/java-gateway-authentication-using-the-json-api/84307 ):

• Should be held in char array instead of String
• Should be cleared after successful login

[imagesc-bot]

This issue has been mentioned on Image.sc Forum. There might be relevant details there:

https://forum.image.sc/t/java-gateway-authentication-using-the-json-api/84307/2

[dominikl]

Due to the whole re-connection logic in the gateway it's just not possible to get rid off the password after login.