update annotate() to match new context manger in mmif-py 1.7.0 #317

mmif-python 1.7.0 added a new "write mode" for MMIF producers (clams apps) to use with many improvement on magic methods to handle some annotation/document properties, as well as guardrails to prevent buggy property value overwrites or mal-attachment to wrong views. We need to pin to new version of mmif-py sdk and update annotate logic to use the new write mode.