This updates JSHintTool to subclass the newer BaseTool, and to use

the newer features it offers (dependencies, improved configurable file

extension handling, and centralized base command building, and

standardized error code/column output).
The new version of the tool also passes a custom JSHint reporter that

returns simple JSON output containing only the information we need for

reporting. This eases parsing considerably, as we can guarantee that any

of the information we use for comments will be completely accurate.
Unit tests were added to cover the new JSHint parsing, and to provide

integration tests. These currently require doing a npm install jshint

in the bot/ directory to run.

Unit tests pass on Python 2.7 and 3.x.
Manually tested the jshint tool with the custom reporter, and parsed

using that data.
There are plans to add integration tests for tools down the road, but

that will require some additional work.