MariaDB4j re-enabled

I originally developed MariaDB4j for Mifos (now Fineract), see https://github.com/vorburger/MariaDB4j#whos-using-it and http://blog2.vorburger.ch/2014/09/mifos-executable-war-with-mariadb4j.html

Over the years, it was (correctly!) moved from a mandatory always included dependency to an optional dependency only included with a certain gradle command line argument. But then over time the separate dev-dependencies.gradle fell out of sync with dependencies.gradle, and MariaDB4j in Fineract is currently broken - the goal of this issue is to re-enable it.

To learn from our past mistakes I let's just entirely avoid the massive duplication of dependencies between dependencies.gradle and dev-dependencies.gradle! How about, instead, we make this mechanism "additive" instead of "replacing"? We can probably simply include (add) only the MariaDB4j dependency on the presence of a certain Gradle/Spring Boot Profile. Not even sure if we need a separate file like dev-dependencies.gradle for that, or couldn't just directly "inline" it into dependencies.gradle and/or build.gradle.

BTW while we're on this, how about we enable this with a dedicated "MariaDB4j" property/profile, and not just "dev"? Because e.g. with FINERACT-931 we have another "dev profile" coming, and one should be able to chose these two dimensions orthogonally; we may want to run -Penv=MariaDB4j,dev (Spring Boot Dev Tools AND MariaDB4j) or just -Penv=dev (only Spring Boot Dev Tools, not MariaDB4j), etc.

nemux given your interest in this topic in https://github.com/apache/fineract/pull/828, would you have any interest in picking this up and adapt your initial PR in that sense?

ptuomola FYI