feat: First steps in linting

[matatk]

• Create two versions of the LandmarksFinder code: one 'standard' and one 'developer' for use in the DevTools (as it's assumed that in future this will be noticeably slower).
• Use the 'developer' version when the Landmarks DevTools panel (in the Element/DOM Inspector) is open.
• The only linting warning logged so far is having duplicate unlabelled landmarks of the same type (ignoring nesting, which seems reasonable).
• The build script was modified to generate the two versions of the scanner as a separate task (though it does it on any run).
• Removed reference to previous "generated-*.js" test-harnessed code.

Future tasks:

• Test the 'developer' mode scanner.
• Localisation.
• Additional checks.