Add gradle support for SPA blueprints

[pmlopes]

Convert the current pom.xml to gradle:

https://github.com/pmlopes/vertx-starter/blob/develop/templates/spa%2Bblueprint/pom.xml

This would allow all SPA blueprints to be used with Gradle too.

[pmlopes]

@jponge maybe you can help using the gradle-vertx-plugin ?

[jponge]

Put it on my todo stack 👍