Added an issue-jwt task

This both helps us check the infrastructure and also opens the door
to more powerful token based authentication.

Conflicts:
	intermine/web/test/src/org/intermine/webservice/server/JWTVerifierTest.java
For some reason these files were missing from an earlier commit.

Adds mechanisms for generating tokens. And an ant-task to check that.

Conflicts:
	intermine/web/main/src/org/intermine/webservice/server/JWTVerifier.java