Builder and Global level environment variables

Currently, environment variables may be set per plan.
For environments with a large number of plans, it would be handy to be able to define environment variables globally for a particular builder or globally.

Users, should be given option to set user environment levels per builder or globally.

Example: My maven is running out of memory, and requires the environment variable
MAVEN_OPTS="-Xms512m -Xmx1024m -XX:MaxPermSize=512m"
to be set.
I would like to be able to set this to a reasonable level for anything built with maven, but don't want to edit 120 plans to do this.

The problem is Bamboo will pick up JAVA_OPTS from command line and pass it down to the build: we should be able to override JAVA_OPTS or any other variable at a global or per builder level.