Introduce expression language in UPDATE queries

[dantleech]

This PR introduces the possiblitiy of setting property values to the result of an expression evaluation using the $row object.

For example:

UPDATE [nt:unstructured] AS a SET a.title = expr('row.getNode().getName()') WHERE localname() = 'article1'
UPDATE [nt:unstructured] AS a SET a.weight = expr('row.getNode().getPropertyValue("weight") * 2') WHERE a.name = 'Product One'

[stof]

why are you dropping the Symfony LTS support for all these components ?

Note that given symfony/expression-language is fully standalone, it is possible to install the 2.4 component in a symfony 2.3 project to use it (you will not have the integrations in places where Symfony itself uses the expression-language of course)