Add ability to enter a new filename

[spacecowboy]

And a bunch of other improvements

Fixes #82

Needs:

• Ability to define a default filename
• Play nice when given a specified path pointing to a file
• Handle if a filename with path is given, e.g. path/to/file. The goal is not to create all folders. In that case, the user knows what he wants and the calling app should handle non-existing dirs

Image of current state