If-Then-Else in $batch requests

Add an optional "if" member to request objects that allows specifying a condition for executing the request depending on the outcome of preceding requests.  The value of "if" is a string containing a boolCommonExpr as in $filter that can reference preceding requests listed in "dependsOn". It replaces the default condition of "all preceding requests listed in dependsOn have succeeded". Filter expression syntax is extended, additional expressions are $<content-id>/$succeeded  to check if the referenced request succeeded  $<content-id>  to reference the response body $<content-id>/<path> to reference a part of the response body Define new property RequestDependencyConditionsSupported ConditionalRequestsSupported for Capabilities.BatchSupportType to advertise this new capability. If a service does not support "if" the conditional request MUST fail and if the conditional request is part of an atomicity group, that group fails and is rolled back.