Add case insensitive sort option for keywords

[chelslava]

Summary

Closes #2521

Adds a "Sort Keywords (Case Insensitive)" option to the keyword context menu, allowing users to sort keywords alphabetically without regard to case.

Changes

treenodehandlers.py

• Added LABEL_SORT_KEYWORDS_CI constant
• Added menu item "Sort Keywords (Case Insensitive)" to resource file context menu
• Added on_sort_keywords_case_insensitive() handler method

ctrlcommands.py

• SortKeywords command now accepts case_insensitive parameter
• Passes parameter to context.sort_keywords()

tablecontrollers.py

• KeywordTableController.sort() now accepts case_insensitive parameter
• When case_insensitive=True, sorts by keyword.name.lower()

Use Case

When keywords have mixed casing:

• Open Browser
• open file
• CLOSE Application

With case-sensitive sort:

CLOSE Application
Open Browser
open file

With case-insensitive sort:

CLOSE Application
open file
Open Browser