Blank searches, update fonts, remove unused code

#620 Add guidance copy for searches with 0 results
#621 Match fonts between data links and supporting docs
#622 Remove preview fetch initialiser

Show released status in search, support inspire HTML links

• show released status in search - #617, #616, #613
• support inspire HTML links - #610
• re-implement Zendesk support - #606

Fix Zendesk support journey

• Fix support form not working - #605

Disable encrypted rails sessions

• Stop creating the redundant rails session cookie - #603

Display dataset contact information correctly on mobile

#602 Protect against spans appearing without content

Use public_updated_at as the "Last updated" date

• Change recent sort option to sort "Most recent" using public_updated_at #599
• Display public_updated_at as the "Last updated" date on search results pages and dataset pages #599

Make public_updated_at available

• Add public_updated_at to Dataset model #599
• Show public_updated_at as the "Last updated" date on dataset pages #599

Improve labelling of licence information

• Improve labelling of licence information - #596
• Add new integration environment - #598
• Fix error for new datasets with govuk_content_id - #597
• Remove ActiveRecord - #600

Update metrics gem, email address rendering

Update metrics gem #594
Improve rendering of email addresses #595

Improved search filters, legacy edit fix, other fixes

• Remove faulty 'not available' label from search results - #593
• Fix link to edit unpublished (no links) datasets - #588
• Add support rake tasks for deleting datasets - #571
• Fix dismissing blue "we've been improving" message - #590
• Fix accessibility issue for sort order button - #586
• Change search filters to only show applicable options - #587
• Fix CSV preview overflowing page bounds - #592