Feature to validate certificate for a SSL connection

[niteesh19]

Custom TrustManager for validating cert digest
Linked to:
https://github.com/edvin/fxldemo-gradle/issues/8

This is implemented as the cacheDir parameter.

Couple of concerns:

1. I have added a new dependency of httpclient v4.5.2 because of which in the pom.xml I had to add maven-assembly-plugin which creates an executable jar with this string appended at the last of the jar name "-jar-with-dependencies". So the maven now basically installs two jars; one fxlauncher-1.0.17-SNAPSHOT.jar and one fxlauncher-1.0.17-SNAPSHOT-jar-with-dependencies.jar. The second jar needs to be referenced by the project fxlauncher-gradle-plugin.
2. I wanted to add a HttpsURLConnection.setDefaultHostnameVerifier() which basically would verify the hostname of the connecting url and the hostname from the "applicationUrl" specified in the gradle build. But I was not able to do it as the HostnameVerifier gets ignored (don't know why.) Should this be present ? Please let me know if you have a way of implementing this. Even if not implemented, this works fine.