Atlassian Template Renderer's memory usage too high

The ATR creates 1 velocity engine per plugin. Each one of these has a fixed-size pool of 20 parsers that end up using a lot of memory.

We should try to reduce this. One option is to plug in a different pool implementation for the parser pools (they are pluggable).

The holy grail would be to reuse 1 Velocity engine across all plugins (actually, one for velocity 1.5 and another for 1.6). Don't know if this is possible but it should be!

To go back to the old behaviour on 5.1.x, pass -Datr.velocity.fixed.size.pool=true as a JVM system property