add control password creating new member

[andreaubbiali]

When you try to create a new member, when you have to put the password there is a control that make sure it isn't too short but when you write in the box "repeat password" there isn't the control if the two password are the same. this commit add it.

[sgotti]

@andreaubbiali Please add the description also in the git commit description not only in the PR description (so your PR will already have a description).

Looking at the code I'll also rephrase this to just "disable submit button when the two passwords don't match also when creating a new member"