store: Break apart Store interface

[adamdecaf]

I'm starting to see store.Store grow beyond a desired size. First it was adding GetInfo(), which wasn't too bad. Afterwords it's becoming cmd/whitelist: fail if we don't have a backup and cmd/chain: Introduce a certificate chain viewer and cmd/create: output certificate chains, bundles, truststores, etc.

I'm proposing to breakup store.Store into:

type Saver interface { 
	Backup() error
	GetLatestBackup() (string, error) // https://github.com/adamdecaf/cert-manage/issues/53
	Restore(where string) error
}

type ListOptions struct { // https://github.com/adamdecaf/cert-manage/issues/172 
	Trusted bool
	Untrusted bool
}
type Lister interface {
	List(opts *ListOptions) ([]*x509.Certificate, error)
}
type Modifier interface {
	Add([]*x509.Certificate) error
	Remove(whitelist.Whitelist) error
}
type Store interface {
	Lister
	Modifier
	Saver
	
	GetInfo() *Info
}

We should probably split things out into subpackages too.. For a java.New(..) for example: #139

The rest can stay on Store and Store should be required to implement Saver and Lister. We just need to expand the options.

[adamdecaf]

I tried splitting each store into it's own package, but ran into cyclic deps.

$ make dist
go vet ./...
import cycle not allowed
package github.com/adamdecaf/cert-manage
	imports github.com/adamdecaf/cert-manage/pkg/cmd
	imports github.com/adamdecaf/cert-manage/pkg/store
	imports github.com/adamdecaf/cert-manage/pkg/store/java
	imports github.com/adamdecaf/cert-manage/pkg/store

[adamdecaf]

It's broken up, but we can probably just get rid of Store totally.