Update module directories to be within their focus directory

[adamsilverstein]

Addresses #46

• Move the webp-uploads module into a images folder in modules.
• Update perflab_get_modules to parse through all the focus folders to look for modules.
• Modules stored in settings now include their focus as part of the module name, for example webp-uploads changes to images/webp-uploads - for this reason, existing users will need to re-enable the webp-uploads module. Not a big concern since only developers are testing this so far.
• Update the docs to reflect the new file/folder structure for modules.
• Remove Focus: from the headers of all sample code and from the webp-uploads module header (only change to module itself)
• Add logic in perflab_get_module_data to use a regex to extract the module type from the module filename (which includes the focus slug as part of its path). Feedback on regex always welcome!

[felixarntz]

@adamsilverstein This looks good except for the logic change for parsing modules, which is now coupled to which focus areas we have defined and also causes tests to fail. Can you update that? I believe some related tests need to be updated as well.

Other than that, only minor comments for e.g. a few oversights that still need to be updated.

[felixarntz]

@adamsilverstein Also, please add the appropriate PR labels and milestone based on #52.

[adamsilverstein]

Thanks for the feedback @felixarntz - I'll work on addressing these points.

[adamsilverstein]

Addressed feedback, updating tests next to work with new setup.

[adamsilverstein]

@felixarntz ready for review:

• module loading now parses all folders in modules
• moved all module tests into focus folders
• used module_dir variable and store slug in module_data
• ensure all tests are updated to pass

[felixarntz]

@adamsilverstein Almost lgtm now! Only a few last minor comments.

[felixarntz]

@adamsilverstein Note there is also #60 being implemented right now. Depending on which of these two PRs is merged first, the other one may need an update.

[felixarntz]

@adamsilverstein I've pushed two small commits here just to rebase and adjust the code from #60 to work with this, since that was just merged (see #58 (comment)).

[adamsilverstein]

@felixarntz - ready for another review when you have a chance

[felixarntz]

@adamsilverstein Excellent work!