Improved settings usability.

Don't ask user to save changes every item switch.
Apply button greyed out when there are no changes.
Advise user he needs a scene before adding a source.
Auto suggest scene and source names.

NameDialog can have placeholder text.
Localize scene number.
Pre-select scene and source text.
Merge pull request #82 from Socapex/master

Small usability enhancements.