Mail translations 2nd attempt

[hakito]

• Remove *-custom.tpl from repo - should only be provided by the user
• Ignore custom translation files
• defaultPath is a fallback path - The name is misleading, as it's not the default.language setting
• Remove dead code
  • DisplayLocalized in SmartyPage was never called
  • DisplayLocalized in Page was only a copy, which is still called, but the languageCode parameter is not used.
• Fix save custom email template for selected language - fixes #424
• Fallback to default lang for missing custom templates ..but only when custom template is available for default lang.
• Add config description
• Change ReservationShareMail property name - It conflicts with the now protected email property
• Fix unit test for updating email template
• closes #416

[hakito]

@effgarces The revert in #441 removed also the changes for #416 and #424. So here is a PR only with the changes for the translations and no refactoring of the email system itself.

I also considered the comment from lucs7 .

The tests are currently failing because of #451

[hakito]

Now checks are green after DST adaption in New York. (See #451)