Add Jackson 2 dependency to Core

The Jackson library's current latest stable release is 2.9.0.

In OpenMRS core, we are including version 1.9.13.

We'd like to upgrade to the latest version, but of course still maintain backwards compatibility.  

Luckily, we should be able to include Jackson 2.x without removing 1.x without causing any issues, from the Jackson... see this note from the Jackson wiki:

"Jackson suite has two major branches: 1.x is in maintenance mode, and only bug-fix versions are released; 2.x is the actively developed version. These two major versions use different Java packages and Maven artifact ids, so they are not mutually compatible, but can peacefully co-exist: a project can depend on both Jackson 1.x and 2.x, without conflicts. This is by design and was chosen as the strategy to allow smoother migration from 1.x to 2.x."