Add difficulty rating to tasks

[fahseltc]

While watching TGH play hunt, he made some good comments and I took note of them for this issue/feature request.

While TGH's main complaint is that the tasks are too easy, most of twitch chat wanted even easier task lists, so I think in general the community wants to be able to have finer control over what tasks are included in their runs.

One of the simplest ways I can think of to implement such a system it to give our existing tasks a 'difficulty rating' attribute on their json object. Something simple like 0-1 (decimal based) or 0-10 (int based) rough approximation of difficulty.
Next, we'd need to come up with more tasks from the community/ourselves to add on either the higher or lower ends of the scales.

Once we have the above 'difficulty rating' all set up, it should be pretty simple to pass another parameter to the backend and select tasks with that rating or lower. We could add a slider or other input to the options section for the user to select difficulty.

[fahseltc]

see #24