provide a way to integrate graphs from another repository

[seebi]

scenario:

/_example%3Atest.nt /_example%3Atest.nt.graph /repo1/_example2.nt /repo1/_example2.nt.graph

• available are two graphs
• new graphs go to the root
• graphs in submodule can be configured somehow

updates to submodule graphs will be updated in submodule directory

[seebi]

another option could be, to integrate other repos with git subtree but this results in the requirement that quitstore is able to r/w graphs from subdirectories.