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
• 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

closes #47 (closed)