feat(episodes): schedule episode with future publication_date by using cache expiration time

- merge publication date fields into one field instanciated with flatpickr datetime picker
- get user timezone to convert user publication_date input to UTC
- remove setPublishedAt() method from episode entity
- add publication pill component to display the episode publication date info
- clear cache after episode insert
- use CI is_really_writable() helper in install instead of is_writable()
- fix latest episodes layout
- update tsconfig to only include ts folders
- update DEPENDENCIES.md to include flatpickr
- add format_duration helper to format episode enclosure duration instead of translating it (causes
translation bug)
- add Time.ts module to convert UTC time to user localized time for episode publication dates
- fix some layout issues
- update php and js dependencies to latest versions

closes #47