Major clean-up in POM's properties

This clean-up was motivated by the impossibility of building the worksheet
against the freshly staged 2.1-M3 for Juno. In short, the wrong ``eclipse.repo`` and
``ajdt.repo`` where provided when building the worksheet for Juno.

With the intent of making the POM easier to understand, I've created a number of new
profiles that should simplify the task of building a release across different Scala
and Eclipse versions.

Last, I took the opportunity to also move to the latest released Tycho, i.e., 0.16.

I'll make sure to update the wiki to reflect the changes.
Merge pull request #116 from dotta/fix-pom

Major clean-up in POM's properties
Updated code accordingly to rename in Scala IDE

Fixes #118
Merge pull request #119 from skyluc/issue/does-not-compiles-118

Updated code accordingly to rename in Scala IDE
Fix compilation due to changes in sdt.core.