Yang-maven-plugin refactored and config attributes and spi adjusted.

Yang-maven-plugin refactored and config attributes and spi adjusted.

Removed project base dir parameter from CodeGenerator
since it can be acquired via additionalConfiguration.
Added resourceBaseDir config attribute that allows resources
to be added to packaged jar.
Added mavenProject config attribute that provides any additional
configuration to code generators if necessary.
Adjusted log levels for the plugin.

Plugin refactored and generate sources test fixed.

Change-Id: Ic3cc1342bb8eb8d6cc374da8af28fa9905ee8fcf
Signed-off-by: Maros Marsalek <mmarsale@cisco.com>