feat: Styling update

[fsbraun]

Description

This PR fixes some styling issues:

• Update to Node 16 for build process
• Two skins: Traditional and django CMS 4
• Rely on FontAwesome 4 (as it does before) if used with Django, django CMS v3
• Use new icons together with django CMS 4
• Correct order of path in folder drop down
• Replace raw id fields by autocomplete fields in admin
• Add left arrow to select file (to date only visible with djangocms-admin-style)
• Align margins to avoid parts of the admin being hidden by scroll bars
• Only offer canonical URL action button if a canonical URL exists

Also, it recognizes "webp" images as such (for upload - easy thumbnail still creates jpg and png thumbnails).

This PR is thought to iron out some usage quirks for the release of django-filer 3.0

Related resources

This PR now contains a django CMS v4 icon set in addition to the fontawesome icon set for pure Django and django CMS v3.

Checklist

• [x] I have opened this pull request against master
• [x] I have added or modified the tests when changing logic
• [x] I have followed the conventional commits guidelines to add meaningful information into the changelog
• [x] I have read the contribution guidelines and I have joined #workgroup-pr-review on Slack to find a “pr review buddy” who is going to review my pull request.

[codecov[bot]]

Codecov Report

Merging #1360 (b2134fa) into master (2780b6b) will increase coverage by 0.10%. The diff coverage is 94.44%.

@@            Coverage Diff             @@
##           master    #1360      +/-   ##
==========================================
+ Coverage   73.15%   73.26%   +0.10%     
==========================================
  Files          73       73              
  Lines        3323     3336      +13     
  Branches      540      542       +2     
==========================================
+ Hits         2431     2444      +13     
  Misses        720      720              
  Partials      172      172              

Impacted Files	Coverage Δ
filer/management/commands/import_files.py	0.00% <0.00%> (ø)
...ile_owner_alter_file_polymorphic_ctype_and_more.py	100.00% <ø> (ø)
filer/__init__.py	100.00% <100.00%> (ø)
filer/admin/fileadmin.py	80.72% <100.00%> (ø)
filer/fields/file.py	64.83% <100.00%> (+0.39%)	:arrow_up:
filer/models/abstract.py	81.51% <100.00%> (ø)
filer/settings.py	79.79% <100.00%> (+0.41%)	:arrow_up:
filer/templatetags/filer_admin_tags.py	91.17% <100.00%> (+0.85%)	:arrow_up: