ListViewController: extract index decision to its own method

[usirin]

This PR introduces a change to KDListViewController with extracting the decision of index depending on lastToFirst option to its own method. This gives us some advantages:

• It can be overriden by subclasses so that those can have their own mechanism.
• Remove hard dependency of lastToFirst.

[sinan]

can we rename the method as getIndex?

[usirin]

@sinan updated.

[canthefason]

I am suggesting to change name of the lastToFirst option. It misleads people (me :) ) in our use case:

For our message pane we are fetching data from api by descending order, and setting lastToFirst=no. And for private messages, again data fetch is in descending order, but this time we set lastToFirst=yes.

In both cases data is fetched in same sorting order, therefore i am suggesting naming lastToFirst option as reverseOrder, which is i think more explicit about its behaviour.

[sinan]

I agree that lastToFirst is confusing, i felt the same way in a few instances. We can change the name but i don't think reverseOrder is any better than lastToFirst, how about
options.order or= 'ascending' # or 'descending'?

[szkl]

Behavior of add and remove methods of list view depends on that option. Order by asc/desc would make me ask order by asc/desc of what or how? I'd rather prefer option name lastToFirst or reverseOrder. Another alternative would be option called direction or orientation with values up and down.