sync refactor: get rid of duplicate action designs
sync refactor: get rid of duplicate action designs

Actions are basically an unnecessarily specialized version of the
`*_full`-methods on StorageInfo. This commit makes the API of Actions
more general and removes the `*_full`-methods.

hobarrera/vdirsyncer,untitaker/vdirsyncer,hobarrera/vdirsyncer,untitaker/vdirsyncer,untitaker/vdirsyncer