The title of this is "allow filetree alternate formats". What that means? By this PR, the +filetree://+ selector
becomes a "generic" selector, capable of decide which kind of file format we are using. This formats are for now
cypress (what you usually know as "filetree") and tonel, but we could add others in the future.
I'm waiting for integration to also submit a PR to update P7.
5 June 2018:
* In Pharo, we are replacing usages of #asIcon with #iconNamed: so I prepared iceberg to this.