Added web api commands for refined conflict resolution.

This PR adds support for merging two features by specifying __OURS__, __THEIRS__, or a new value for each attribute of a feature.  This is currently done by posting a json object that configures the merge.  The command performs the merge and returns the object Id of the newly created feature.

A second web api command was added to resolve a conflict by specifying a particular object ID.

The workflow for resolving conflicts using this method is to use a web client to present the user with the conflict, allow them to pick and choose attributes from ours or theirs, or supply values of their own.  Once the user is satisfied, create a post request to the web api with their choices.  The web API will then return the new feature ID, which the client can then use to resolve the conflict.