CLN: refactor Styler._translate into composite translate functions

[attack68]

This composites Styler._translate() into:

def _translate():
    ...
    self._translate_header()
    ...
    self._translate_body()
    ...

where the _translate_header() and _translate_body() methods are given some documentation explaining what they are building. The code is not fundamentally changed, but variable names are renamed to add clarity to match the documentation and loop comprehensions replace for loops where possible.

Some tests are minimally altered since the generic _element method now returns more dict keys for some elements.

[jreback]

is there a _translate_footer() (maybe currently unused)?

[attack68]

is there a _translate_footer() (maybe currently unused)?

No because the html element <tfoot> is not used in the jinja2 templates.

It might be useful for easily adding styling of a totals row for example in the future, albeit can be done currently, its just not that easy.

[jreback]

looks good a question

[jreback]

so these are just additional attributes that currently are defaulted?

[attack68]

yes the new _element function outputs 5 dict keys by default for each cell.

Previously almost all cells needed these 5 and a few only had 3 keys like column header cells. There is no harm adding them, and actually might make future dev easier, for example a hide_headers() method to complement the hide_index method can hook into the is_visible additional key.

[jreback]

thanks @attack68