FileAppender in LoggerContext is optional

Logging to the file now can be turned off in annotation processing
options. It is still on by default.
use Set instead of List in OnViewChangedNotifier

this avoids @AfterViews annotated method to be called multiple times e.g. when re-adding previouse @EFragment instances
Merge pull request #1275 from dodgex/1264_use_set_instead_of_list

use Set instead of List in OnViewChangedNotifier
Merge pull request #1110 from WonderCsabo/fileAppenderOptional

FileAppender in LoggerContext is optional