BREAKING CHANGE: URI now contains complete host!

Did quite a lot of work again. One of these commits will break existing accounts and  some steps are necessary to get them working properly again. Read in the commit message. The change might solve the issue with multiple accounts on the same device. But it is required for more complicated redirects (mostly the .well-known/caldav kind of redirects, they often change the hostname).

I also found & fixed the issue with owncloud.. a stupid typo (lenght). 

This now also works with yahoo (url: caldav.calendar.yahoo.com, calendar and contacts might work, issue with umlaut, see reported issue) and fruux.com (url: fruux.com).

Some commits are code maintenance.