Create fat jar for transaction manager

Due to the incompatible guava version in HBase (12 instead of 13), the transaction manager will not work by just pointing it to the HBase lib dir. A reasonable alternative would be for Phoenix to build another fat jar specifically for the transaction manager which includes all necessary dependencies (namely guava 13). Then the bin/tephra script (we should rename that to tephra.sh perhaps?) would simply need to have this jar on the classpath.