FLUID-5210: Added a merge policy

Adds a merge policy to the composite panel for merging selectorsToIgnore. This is necessary for the case where the composite panel has defined selectorsToIgnore. When the auxBuilder is run it needs to add selectorsToIgnore for the subpanel containers.
Merge branch 'FLUID-5210'

* FLUID-5210:
  FLUID-5210: Added a merge policy
FLUID-5211: Pass down the addtional options defined in the auxiliary schema for subpanels to constructed grade.
Merge remote-tracking branch 'cindy/FLUID-5211'

* cindy/FLUID-5211:
  FLUID-5211: Pass down the addtional options defined in the auxiliary schema for subpanels to constructed grade.