Add metadata to CI outputs and rename tg to tasmean

[eyvorchuk]

Charles requested a few enhancements to the on-demand downscaling tool that would be easiest to implement through chickadee.

• Add the following global attributes to the metadata for CI outputs:

// global attributes
		:institution = "Pacific Climate Impacts Consortium (PCIC), Victoria, BC, www.pacificclimate.org" ;
		:contact = "Pacific Climate Impacts Consortium" ;

• Rename the tg variable initially created by finch.tg for computing tasmean to tasmean.