Upgrade to cucumber 115

Hi,

My changes are big enough that it might be delicate to merge them. Still, here they are. The new features are:

 a) allow to specify SourceSets that would contain Cucumber features and step definitions
 b) if 'src/cucumber' and (a) is no set, a 'sourceSets.cucumber' is automatically defined (with the corresponding configurations)
 c) if neither (a) nor (b) are set, revert to previous behaviour: assume a "cucumberRuntime" configuration
 d) when source sets are defined, they contribute their resources dirs to the features locations, their source dirs to the glue dirs. In addition, their output classes dirs are automatically scanned in order to specify package glue dirs (e.g. "classpath:package.name").
 e) upgraded to Cucumber 1.1.5 although I have a feeling that this version breaks the integration with Idea (it seems to be compatible with v1.0.11...).

--> these features allow to vastly simplify the configuration of the plugin, esp. if one follows conventions.
--> I tested it was possible to mix step definitions of different languages (I tested Groovy + Java)
--> anything configured via CucumberConvention should still override automatic behaviors

Voila.
Philippe

PS: I changed the version just for my tests. Don't mind them.