Improve enforced password link function and allow to send link by mail

[thetuxinator]

Thx for fixing the enforce-password problem, By trying to use it for my usecase, i added a customlink called testfolder8 , for my usecase i discovered the following issues: There is no way to generate a password (like when you use "share by mail" directly) when creating a custom link using this extension, the "share by mail" function does still use a random link. Maybe a good fix would be to add a direction option of "share by mail with custom link"

thx in advance for any effort