iOS certificate and certificate passphrase handling

[Larusso]

Description

I want to change the handling of certificates needed for a build in a few ways. To get us started I defined a simple default FileTree which picks up any *.p12 file in the project. To gear us towards a secure CI and local setup I would change the default value to be read as other values from the Environment and Properties. This gives a CI system like Jenkins the possibility to inject a certificate and also the matching passphrase. I don't have a definite way how to provide certificate/passphrases pairs at the moment.

Next to usability reasons a integration test setup would be way easier to create that runs on a CI system.