(GH-525) Extend AppConfiguration class
(GH-525) Extend AppConfiguration class

Using the new attributes, to distinguish between a feature and a config
setting, as well as add the new configuration property for how long
before invalidating the OutdatedPackages cache.

gep13/ChocolateyGUI,gep13/ChocolateyGUI,chocolatey/ChocolateyGUI,gep13/ChocolateyGUI,gep13/ChocolateyGUI,chocolatey/ChocolateyGUI,chocolatey/ChocolateyGUI,chocolatey/ChocolateyGUI,chocolatey/ChocolateyGUI,gep13/ChocolateyGUI