Created a how-to page

The purpose of this page is to provide some help with common questions related
to direct usage of the Scala IDE, or any tool that developers may be using in
conjunction with the Scala IDE (e.g., build tools such as Sbt, Maven, Gradle,
ecc).

You may ask why creating a new page when we already have a ``Frequently Asked Questions`` one. I don't have a rational explanation for this, but I feel the ``Frequently Asked Questions`` is not a good fit. I think it's messy enough as it is, and adding also a ``How To...`` section would really not help.