introduce depth limit

[don-han]

set the level of how deep a crawler goes

Assumption: Most interesting information exists at the nearest depth to the base url

Reasoning: As you go deeper into the website, the information becomes more specialized to specific function such as the integration service #2 such that the information no longer applies to the description of the institution

[don-han]

Now that scraper has both the tier limit and the page request limit, I don't think we need a third limitation.