In this commit we enhance our current template linter to detect
duplicate ids and report them during lint checks. html_branches.py
was topped up with a new function build_id_dict for the purpose.
Also the get_tag_info function in same file was updated to parse
ids and classes more robustly in cases of template variables.
split_for_id_and_class function was added to serve this purpose.
Unit tests for both the functions were created under
tests/test_html_branches. Also a directory under tests called
test_template_data was created to hold templates for testing under
newly created functionality.
check_templates was modified to print to console any duplicates
detected.
showell reviewed my commit and helped me out.
Fixes#2950.
Anders Kaseorg
adnrs96