apply license gradle plugin

[sdelamo]

This PR applies the Gradle License Plugin. The plugin contributes a gradle task downloadLicenses which generates a license report of every dependencies.

The plugin is applied to subprojects and the root project to get an aggregated report.

./gradlew downloadLicenses
open build/reports/license/license-dependency.html

[CLAassistant]

All committers have signed the CLA.

[matrei]

To prevent bloating the root build file, could we extract this to a new file, for example: gradle/dependency-licenses.gradle?

[sdelamo]

To prevent bloating the root build file, could we extract this to a new file, for example: gradle/dependency-licenses.gradle?

@matrei I did that in 9e7b153

[matrei]

Nice, now just one more thing I saw (I'm a bit allergic to complex build files):
As we already have an allprojects block in build.gradle, we can apply the gradle/dependency-licenses.gradle file there, so we don't have to do it in multiple places:

allprojects {
    
    apply from: rootProject.layout.projectDirectory.file('gradle/dependency-licenses.gradle')

    ...
}