API: remove `.set_tooltips_class` incorpate to `.set_tooltips`
`.set_tooltips` and `.set_tooltips_class` are introduced to 1.3.0.

Just realised it seems a bit pointless to have two api functions:

- [x] remove `.set_tooltips_class()` and `._init_tooltips()`
- [x] include the `css_name` and `props` arguments in `.set_tooltips` for same functionality.
- [x] no api break since these functions have not yet been released
- [x] make argument names more consistent with other Styler methods.
thanks @attack68 very nice