Expose Axis tier intervals.

Right now there is no endpoint to manipulate possible time intervals for major and minor ticks.
With this PR I introduce an API endpoint to provide custom time intervals.
To cover basic scenario I provide function, which easily can filter existed interval within some range. It might go directly to previously mentioned API, which will accept array or desired range.

Close #1212.
I'm not sure what the correct TSDoc for interfaces is. I wonder if it'd be appropriate to include the type, similar to the documentation for methods? Ex:
```
{D3.Time.Interval} interval - A time unit associated with this configuration (seconds, minutes, hours, etc).
```