Added requireDefaultMessagesFile setting.

Added a new requireDefaultMessagesFile setting. Removed the
MessagesAndFile class from PlayMessagesMessageParser, and moveds the
Messages class to PlayMessages. Minor build tweeks.
Implemented checkApplicationLanguages functionality.
Removed generateScala setting. Fixed log messages.

Removed generateScala setting. Split the checkAndGenerateTask to enable
removing the generateScala setting. Updated log messages for consistency
and ease if reading.
Sort out the build version.

The build version is needed in the build and by the plugin when
depending on the library. I believe these cannot be merged. Updated the
PlayMessagesPluginJava autoImport comment.
Updated change log for release.