* Fix a couple of typos
- In the main ReadMe.md
- In onEach template's doc

* Update generated source code

- Actualize build requirements and steps
- Extract Gradle plugin readme to the corresponding folder
- Rewrite Libraries and Maven Tools readme

#KT-20995 Fixed

update README.md with direct download link to IntelliJ IDEA latest version

This reverts commit c92408ee

This reverts commit 722345d1

This section is valid before kotlin is built by gradle. Since there is
no working directory setting in run configuration, we need to delete
this document

* Improve information regarding running tests that load resources

Figuring out how to run isolated generated tests is not imidiately straightforward.
This clears up confusion by throwing a more helpful error in the tests and
adding a section to the ReadMe.

* Cleanup ReadMe and comments after review feedback

Reduce the barier to entry for working on Kotlin by providing a
download link for the MacOS JDK6 in the ReadMe.

http://kotlinslackin.herokuapp.com/ is down, replaced with http://slack.kotlinlang.org/

No soft-wrapped words.

Also update links and overall readme structure.

Slight improvement of wording in the section that explains the benefits of contributing code examples for library functions

Misc: Configure IDEA Ultimate dependencies