Support Kotlin Gradle projects

[saschpe]

To generate a license report for a non-Android project, the java plugin has to be applied even for Kotlin projects. Thus, the following does not work:

plugins {
    id("com.jaredsburrows.license")
    kotlin("jvm")
}

However, non-Android projects that use Kotlin are 100% Java-compatible. The workaround is:

plugins {
    id("com.jaredsburrows.license")
    kotlin("jvm")
    java // For `license` plugin only
}