Checks and fixes permissions of home folder and config file to be editable and writable only to the owner when using macosx or linux.

Changes the method used to load default properties file on Android.
Closes the stream after loading.

The file is named jitsi-default-overrides.properties and it allows a
deployer (system administrator) to keep a separate set of locally
define properties, different from the ones the come with the client.

This commit also allows for zero length override property values.

This doesn't change anything semantically since the exceptions could
have already been thrown. They were just removed from the signatures in
an earlier commit and that might have been an omission during
refactoring.

Moves the ConfigurationService and FileAccessService implementations from Jitsi into libjitsi. Silences handled exceptions in libjitsi by converting them into Logger informational messages.