Move WebApplication initialization code from bootstrap (old index.php) to WebApplication class constructor.
Add abundant comment on DropboxServiceProvider class
Restyle comments on ConfigServiceProvider and remove "debug" from possible keys in the config file
Add comments on services that will be eventually provided by DropboxServiceProvider
Add usage comments on DropboxServiceProvider
Restyle ConfigServiceProvider to have [config] registered at once with lazy evaluation
Define services provided by DropboxServiceProvider. Rename config variable "code" to "authCode"