Groovy naturally supports many dynamic features that we don't benefit for now but cost performance loss, in this patch we compile our Groovy-based DSL scripts statically to optimize performance.
* Add `sum` function in meter system
* Fix minor potential bug and reformat some codes
* Fix a bug
* Use Set to hold the {aggregate,scope} labels as same labels maybe added by multiple aggregation functions
* Separate downsampling function and revert unnecessary codes
kezhenxu94
zhang-wei