add `StoreExport` and `StoreImport` class

[kazurayam]

A user will have a store directory of a project locally on his/her machine. In the local store, he/she will create many artifacts (directory trees of Materials, HTML Reports). Now let me assume 2 or more people work as a team. They would want to share the products of their work. Therefore it should be possible to create a remote store somewhere. They will export their own artifacts from the local store into the remote store. And the will import the artifacts from the remote store into the local store when necessary.

So I need 2 utilitiy classes:

• com.kazurayam.materialstore.manage.StoreExport that transfer files from the local store to the remote store
• com.kazurayam.materialstore.manage.StoreImport that transfer files from the remote store into the local store.

[kazurayam]

planned at the ver 0.11.4-SNAPSHOT

[kazurayam]

done at 0.11.4