Prevent password managers to overwrite passwords in reseller / client and mailbox edit screen (fixes #4030)

- mail accounts not locked when client locked
- mail account sending and receiving lock separated
- fixed error in query
- fixed wording to match separeted locks

- Random password length: by default, generated passwords will have a length between 10 and 15 characters (instead of a fixed length of 10 characters).

Merged revisions 3049-3051,3053-3054,3058,3070,3074-3077,3082,3086-3088,3091-3092,3094-3095 from stable branch.

Fixed: FS#1712 - Welcome email in multiserver setup problem (welcome mail not send because MySQL delay)

Updated english languages files
Updated czech languages files

Added missing strings in some templates to english transalations

Fixed: FS#778 - mailalias has priority over mailbox if they both exist. Added a error message that prevents it to add a alias or forward when a mailbox with the same email address exists.

fix for local characters not encoded properly in welcome-email. remove trailing empty lines from finnish language, again...

Fixing the way some User Interface text was used. For the quota on a mailbox I added 'in MB' so that the user knows what units the quota is in.

Fixed: Several php notices for undefined indexes.