Provide top level methods to set custom http handlers

[sarahsnow1]

Overview

This is the first of two PRs needed to bring first class support for providing custom http headers and parameters to search, routing, and tile requests. This work adds MapzenSearch#setHttpHandler(MapzenSearchHttpHandler ), MapzenRouter#setHttpHandler(MapzenRouterHttpHandler ), and MapzenMap#setHttpHandler(MapzenMapHttpHandler ) methods.

Proposed Changes

• Adds top level APIs to set custom http parameters and headers
• Adds relevant test coverage
• Adds SDK LogLevel enum for mapping to internal implementation log level (future PR will provide ability to set log level on search and map handlers as well Allow setting custom log level for search and tile requests #445)
• Updates MapzenRouterHttpHandler to allow setting base url and log level

A follow up PR will provide support for pulling the API key from MapzenManager automatically (#444)

Closes #443

[sarahsnow1]

I'm going to merge this so I can start on #444. I'll address any issues in the PR for that (related) work.

[tallytalwar]

👍