Broken API links in the three Transaction Service topics

[gedinakova]

Steps to reproduce:

1. Navigate to Transaction service topic
2. Check the links in the main and the two child topics

Result:
API links to "IgxFlatTransactionFactory" and "igxHierarchicalTransactionService" are broken

Expected result:

The proper API members should be added in order to be able to link into the API docs.