playlist: implement natural sorting as alternative to alphabetical

[jclement46]

There are 2 issues here, alphabetical and numerical. I have slides that are numbered according to the original codes. If I have 3 slides that are A1,a2,A3 sView shows them in order A1,A3,a2 while windows lists them in the correct order which ignores the case. This should be an easy fix, but then there is the issue of other Western languages with diacriticals. Yes, the a2 should be A2, but there are often slips in typing which are difficult to find.

The other issue is that the following pictures A1,A2,A3,A11 will be displayed as A1,A11,A2,A3 while Windows lists them in the correct order. This may be more intractable to fix. Windows fairly much follows the usual rules. The workaround has been to have A01,A02,A03,A11.

[gkv311]

This is called "alphabetical" and "natural" sorting. sView currently implements only "alphabetical" one.
https://en.wikipedia.org/wiki/Natural_sort_order