Merge Attribute definition and XVariableDeclaration in SARL.xtext

[srodriguez]

Attribute and XVariableDeclaration have the same definition. We should have only one for both.

[gallandarakhneorg]

Currently is it not possible to define a static final variable.
If we merge Attribute and XVariableDeclaration, it will avoid to support this particular type of constant.

[gallandarakhneorg]

Now, the inferrer is appending the keyword "static" when a val is directing initialized:

val a = 123

[gallandarakhneorg]

We may merge the two grammar rules safely. It will cause a large refactoring of the inferrer, the unit tests, but not so hard.

[srodriguez]

I am not sure that we will need new modifiers shortly, but meanwhile we'll put the issue in stand-by

[gallandarakhneorg]

Ok, I have no objection for merging attribute and local name definitions.

[gallandarakhneorg]

This issue is deprecated since the issue #34 will introduce the attribute definition from Xtend.