* abi-gen: inline @0x/abi-gen-templates
And use those inlines by default, relieving caller of having to specify
--template and --partials all the time.
Simplify abi-gen usage in all package.json's, omitting --template and
--partials to defer to the defaults.
* abi-gen: Update CHANGELOG.json
* contract_wrappers.py: be a user of abi-gen