FormContainer variable does not recover after end of formContainer macro

I suggest that `$formContainer` variable should be recovered after end of `formContainer` macro. It is not prefixed with `_` so I can use this variable in code.

Example in commit's test: https://github.com/MilanPala/forms/commit/d573f2890f466178fc7503e778dd6f7a778488e4
