V2 -> V3 testing progress

[Cantor, Scott]

Fair amount of progress made, and I made a number of installer
improvements to smooth things out, but there's one major blocker Rod and I
will need to ferret out a solution for [1] before I can move on to real
testing.

I just committed a minor but fairly visible change that renames creds back
to credentials because changing the location of keys and certs breaks
every upgraded configuration for no good reason because the old
relying-party.xml will reference credentials/idp.key and idp.crt in most
cases.

I also put idp.war back in war/ so that people don't have to update every
existing context descriptor, again for no good reason.

The source and overlay trees are now webapp and edit-webapp, which is
clearer IMHO.

-- Scott

[1] https://issues.shibboleth.net/jira/browse/IDP-488