Orphaned staging graph on ModelLoad

[dlamoris]

On ModelLoad - the loaded graph replaces the previous staging graph of a branch and the previous staging graph is orphaned .
https://github.com/Open-MBEE/flexo-mms-layer1-service/blob/develop/src/main/kotlin/org/openmbee/flexo/mms/routes/gsp/ModelLoad.kt#L440

There is a separate but related issue to how the ?_interim lock is added/deleted during a ModelLoad/ModelCommit - during the call to genCommitUpdate (used by both ModelLoad and ModelCommit)

• an ?_interim lock was supposed to be created to point to the previous ?model snapshot
  • this was supposed to point to ?model from the 'where' clause, which comes from BRANCH_COMMIT_CONDITIONS in Conditions.kt
  • ?model was never bound because the condition morc: was supposed to be ?baseCommit (and this clause was commented out at some point)

//                    # optionally, its model snapshot
//                    morc: ^mms:commit/mms:snapshot ?model .
//                    ?model a mms:Model ;
//                        mms:graph ?modelGraph .
//                }

• at the end of ModelCommit/ModelLoad, the ?_interim lock gets deleted as well as the model graph - but graph delete never worked because it didn't get related to the right model, plus there was a syntax error (the syntax error is fixed in the feat/ldp branch, link to syntax error issue malformed query exception #130 )
  • in addition, this doesn't check if there are other locks pointing to the ?model (which would prevent the delete since a commit lock is automatically created after each model load/commit)

Proposed fix would be to delete the previous staging graph on model load instead.

Relevant files and lines:

• BRANCH_COMMIT_CONDITIONS in Condtions.kt
  https://github.com/Open-MBEE/flexo-mms-layer1-service/blob/v0.1.2/src/main/kotlin/org/openmbee/flexo/mms/Conditions.kt#L75
• genCommitUpdate is called https://github.com/Open-MBEE/flexo-mms-layer1-service/blob/develop/src/main/kotlin/org/openmbee/flexo/mms/routes/sparql/ModelCommit.kt#L170, https://github.com/Open-MBEE/flexo-mms-layer1-service/blob/develop/src/main/kotlin/org/openmbee/flexo/mms/routes/gsp/ModelLoad.kt#L440
• genCommitUpdate https://github.com/Open-MBEE/flexo-mms-layer1-service/blob/develop/src/main/kotlin/org/openmbee/flexo/mms/routes/Model.kt#L52
• cleanup in ModelLoad https://github.com/Open-MBEE/flexo-mms-layer1-service/blob/develop/src/main/kotlin/org/openmbee/flexo/mms/routes/gsp/ModelLoad.kt#L562
• and ModelCommit https://github.com/Open-MBEE/flexo-mms-layer1-service/blob/develop/src/main/kotlin/org/openmbee/flexo/mms/routes/sparql/ModelCommit.kt#L329