Fixed error when compiling filter script if the user imported and appended filter rules to existing rules. The first imported rule was not being assigned an operator, which resulted in a script compilation error.
Issue: MIRTH-2746
Removed ErrorConstants

When generating error messages, connectors now use the name of the connector properties (ie. Channel Writer). Serializers, validators, and VMRouter use the simple name of the class (ie. ER7Serializer). Javascript related error messages use names such as Preprocessor, Filter, Transformer, Response Transformer.
Issue: MIRTH-2677
Moved MigrationException from com.mirth.connect.server.migration to com.mirth.connect.model.util since it is referenced by ImportConverter3_0_0, which is run on both client and server.
Issue: MIRTH-2733
MIRTH-2753, MIRTH-2718: Added the ability for the server to catch deserialization exceptions for channels and still allow them to be passed into the cache (and to the client). This is done by wrapping the invalid channel XML into an InvalidChannel object (the cause is passed in as well), which extends Channel.

ObjectXMLSerializer now registers ChannelConverter, which extends MigratableConverter. The converter intercepts Channel objects being marshalled/unmarshalled. When deserializing, the converter first tries to delegate to the superclass. If that fails, the original XML and Throwable are passed into the InvalidChannel constructor and that is returned instead.

ObjectXMLSerializer also intercepts exceptions coming from ImportConverter3_0_0 and wraps Channels in InvalidChannels there too.

MIRTH-2752: DefaultChannelController.updateChannel now does null checks before trying to set the connector plugin versions.
Added stack trace to the error message when a connector class fails to load on the Administrator.
Issue: MIRTH-2754