factor operation state out of uniter packager
make serialization explicit, update field names
more meaningful names for uniter fields; trivial consequent rearrangements for line length
put top-level test funcs in right place
fix imports, package names
silence stupid warning on push
second attempt at silencing stupid warning on push
Merge pull request #918 from fwereade/ops-queue

behaviour-preserving uniter refactoring

* pulled TestPackage funcs out into package_test.go files
* extracted Op, OpStep and State from uniter into new operation package
* made related type/field/method names more clear/readable
* fixed line lengths broken by the above
* meaningless change to bundles_test.go to fix a push warning