Mail methods refactor

Mail method should be refactored so that:

• We avoid duplicated code in mailAccount/mailGroup/sympaAliasPartage
• We avoid connecting to the mail server when it’s not needed
• Even lazily load quota info to speed-up account edition?
• Support correctly server change (partly done)
• Maybe improve server change with the same method?
• Hide non-supported fields (or check that this is the case already)