Support Kotlin MPP (Multiplatform Projects)

[slavaatsig]

With a release of Kotlin 1.3 and improved support for multiplatform projects in Gradle, there were some changes in directory structures that should be considered by the plugin.

• Official directory structure conventions
• Multiplatform library official Kotlin documentation
• Default Kotlin MPP layout with Gradle

[yuanqingfei]

I met such problem. It cannot find main Verticle which defined in MPP mainJvm