Update recorded responses for filter_groups_index
Update APIv3 changelog about filter groups index caching
Merge remote-tracking branch 'origin/update_changelog_filter_groups_caching'
Style changes at index page

* Change font-family of h1
* Change icon font in "What can I do with Skroutz" list
* Change font-size and color of text in sidebar
* Style text in footer
Minor style changes for css components

* Decrease font-size in sidebar elements
* Change styles of h1, h2 and h3
* Fix font-size and padding in panel's list
* Increase font-size of preformatted code