Feature/updating base files

[harryfinn]

Updates to Erebus theme files and minor structure tweaks:

• Removes .sass-lint.yml as requires ruby dependency and can be replaced by stylelint
• Removes gulp file and associated base js and css files generated by the build process as now handled by webpack
• Renames assets folders and add autoloads to images folder and use scss glob imports
• Updates webpack config for javascript and stylesheets loading plus package dependencies

[jezemery]

All looks good to me

[harryfinn]

All looks good to me

Thanks @jezemery - have got some tweaks to Zeus to make too so will do a final test on both sets in a new project before making this PR 'active' again with a view to merge if all are happy

[HobbitCodes]

Nothing mental going on, looks good to me bud.