ReverseRelationName in inccluded admin form element

[davoreric]

If included admin is used with "reverseRelationName" in options then calling "setMainRelationReference" method will not find correct fieldName as is set in "reverseRelationName" options

Correct fieldName usage

trim/src/js/formElements/includedAdmin.vue

Line 199 in e0bf1a3

const reverseRelationName = this.relation && this.relation.reverseRelationName;

Incorrect fieldName usage (it is not accounts for reverseRelationName)

trim/src/js/formElements/includedAdmin.vue

Line 360 in e0bf1a3

const fieldName = this.resourceModel.getType();

[davoreric]

Added pull request #18