Removed openText from Editor

The method didn't really fit in, and added a fourth dependency to Editor.

File should still be the recommended used Model, Text is just a convenient one,
in case someone.
Moved FileFactory into Filesystem

Filesystem already knows how to convert an array of lines to a string,
so the responsibility to convert a string to an array of lines should
get back to it.
Merge branch 'fix/openText'
[1.0.0-beta1] Updated CHANGELOG