Java 11 compatibility & Spring boot 2.1

[RLejolivet]

The goal of this PR is to allow full Java11 compatibility:

• Projects running with Java11 with no warnings
• Projects building targeting release 11
• Blossom build with Java11, including release targeting to 11 (even if this isn't the case for now)

Changes to this effect:

• Upgrade to Spring Boot 2.1
• Add dependencies to Java modules that are no longer part of the JDK: javax.annotation, jaxb-runtime
• Upgrade maven plugins to versions that support Java 11: Jacoco 0.8.2, maven-javadoc-plugin 3.0.1
• Security upgrade : apache tika to 1.20
• Camunda starter from 2.2.0 to 3.2.0 to work with Spring Boot 2.1
• Removed implicit bean overriding for MessageSource since bean overriding is disabled by default with Spring Boot 2.1, instead extending the default MessageSource

Question:

• [x] I chose org.glassfish.jaxb:jaxb-runtime for JAXB implementation, as it was used on some of my projects anyway. I am debating sticking to com.sun.xml.bind:jaxb-impl instead, as it is the default implementation that was packaged with Java

[coveralls]

Coverage remained the same at 54.005% when pulling e5757109b0eb20ec8c411d10649aaa8e552baf2f on RLejolivet:java-11 into c197217604e172ae75a26db3775659d35b1fdb4b on blossom-project:master.