Defined the content type name for Play Template files

Fix #62
Add a few more syntax classes for coloring.

* 'symbol
* numeric literals
* multi-line strings

Fixed #44.
Merge pull request #63 from dotta/issue/no-content-type-for-play-template-file-62

Defined the content type name for Play Template files
Updated scm config in POM required to extract the GH hash
Adds a preference and an project preference page

The preference is initialized with framework defaults (play.api.templates._, play.api.templates.PlayMagic._).
It can be overriden at the project level, in the project properties.
Changes are not applied directly, as we are currently lacking a real builder.

Fix #35.
Automatically add Scala nature when opening Play2 Template editor

Java Play2 Template project don't have the Scala nature by default, and this
caused an exception to be thrown whenever the user tried to open a Play2
Template editor because the editor needs access to the ``ScalaProject``
facilities.

The implemented solution is to automatically add the Scala nature if a project
doesn't have it.

Note that ``TemplateCompilationUnit.scalaProject`` is no longer ``lazy``
because I want the code to fail fast if a ``ScalaProject`` cannot be created.

Fix #33
Minor clean-up in code and POM

* Removed unused import in ``RouteTestSuite``.
* Added explicit return type on public methods.
* Remove comment in POM about Play 2.0.x support.
Merge pull request #56 from dragos/issue/more-syntax-colors-44

Add a few more syntax classes for coloring.
Merge pull request #43 from skyluc/issue/additional-imports-35

Adds a preference and an project preference page
Merge pull request #64 from dotta/issue/detect-missing-scala-nature-33

 Automatically add Scala nature when opening Play2 Template editor