Enhance safe template linter

- Check includes for Mako templates
- Check display_name_with_default_escaped uses
- Add exceptions for Underscore and <%=
- Skip templates that are Django and not Mako
- Add pragma to disable errors
- Enhance unit tests
- Remove violation mako-js-string-missing-quotes
- Refactor line processing into StringLines

scripts/tests/templates/includes/include_safe.html

+## Mako template with safe by default page expression
+<%page expression_filter="h"/>

scripts/tests/templates/includes/include_unsafe.html

+## Mako template with no safe by default page expression

scripts/tests/templates/test.html

+<%include file="./includes/include_safe.html" args="message" />
+
+<%include file="./includes/include_unsafe.html" args="message" />
+
+<%include file="bad_file_name.html" />
+
+## safe-lint: disable=mako-include-with-violations
+<%include file="bad_file_name.html" />