Update Employee Registration page to use bh-* components

[jniles]

The Employee Registration page (link) has a fair amount of refactoring that could be done to remove imports and replace with bh- components. For example, it would be appropriate to update the controller to remove the import for Services and replace it with bh-service-select. These updates would simplify the main controller code.

Specifically, the following could be added, removing their custom counterparts:

1. bhGradeSelect (link)
2. bhServiceSelect (link)