StringConstants: Move True and False strings here

This also makes them translatable.
coala: New welcome string to demonstrate Voice Output
StringConverter: Add and use it
StringConverter: Add more conversions
Outputter: Add show_annotations ()
AnnotationResult: Add object
SettingsTest: Add SettingsTest
SettingsTest: Improve SettingsTest
StringConsants: Add more true/false strings
Merge pull request #42 from sils1297/various

Various changes