Make gradle tasks incremental

[aasitnikov]

In Gradle, task can become incremental, if it properly declares it's inputs and outputs. Configurations (like "embed") can also be task input.

Currently most of the tasks, created in RProcessor class, declared using Runtime API. Although it's possible to declare inputs and outputs with this api, it's better to refactor this tasks into separate classes, as described in this section of gradle documentation.

Also it would be nice to implement Task Configuration Avoidance, as it further enhance build speeds.