Support multiple schema locations

[taneliang]

Currently, we assume that all schemas are stored in a "./src/gents" folder. We need to support multiple schema folders to support larger apps.

• Allow gentgen to look in multiple directories. It is currently hardcoded to "./src/gents" (Implement proper gentgen CLI #3).
• Modify file import generation to somehow look for referenced schemas (as we assume all schemas are stored in one folder, we currently assume the component can be found at the relative path ../<entity class>/)