Share intellij idea settings in the team

Motivation
----------
In order to make it easier to bootstrap with project it will be good if
some projects settings will be shared in the team. It will also allow
perform tasks such full project tree cleanup.

Modification
------------
Import .gradle project once using IntelliJ Idea. The IDE can watch and
sync settings if needed (e.g. change of versions). To setup .gitignore
rules, official support ticket was used:
https://intellij-support.jetbrains.com/entries/23393067

Result
------
No need to import .gradle project to idea each time developer cleans the
tree or setups new machine.

Change-Id: Ib7a24300873857a76b01a1e4a14d20239bafe8bd
Reviewed-on: http://review.couchbase.org/42718
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Michael Nitschinger <michael.nitschinger@couchbase.com>