*.gradle: some changes

* Update msg-simple dependency.
* Introduce the prepareIdea task.
* Do not bundle the fat jar, it is just too big.
Move group/version/other into build.gradle
Update jackson-coreutils dependency (and therefore jackson as well)

Now jackson 2.2.x.
.gitignore: add IDEA's output directory
BUILD.md: add instructions for IDEA users

I don't use eclipse.
Add JsonParser.Feature support to LoadingConfiguration and URIManager to allow loading of nonstandard JSON syntax including comments, single quotes, unquoted field names, etc.