Add shared settings for IntelliJ IDEA

Including new 'ideaSettingsJar' gradle task; see comments in
.idea/.gitignore and .idea/exported_settings/README.md for details
Enable annotation processing within IDEA

This eases the process of getting started with Lombok. Installation of
the Lombok IDEA plugin is still required.
Add unzipIdeaSettingsJar gradle task

For convenience when upadating shared settings.
Configure IDEA for unix line endings
Configure IDEA import settings