Closes T848

Related T848

implement lines highlighting feature for browse content views (either by clicking on line numbers or using an url fragment like '#Lx' or '#Lx-Ly')

normalize HTML view titles in browse

display visit date when browsing a swh object in an origin context

get rid of that agressive yellow background in the html browsable swh-web api and use the same color as in the browse application

ensure that the autoreload feature of django dev server works when modifying any swh-web source files

closes T491

drops Debian jessie support: remove previously introduced hacks and workarounds in order to support it + update requirements and debian/control

closes T802

raise exception when requesting to browse an origin directory/content/history but there is no existing swh visit

ensure display of textual content not encoded in utf-8 in browse content views + add encoding to content metadata

wrap swh object metadata in HTML pre tag for a better display of textual content in browse web application

closes T828

update documentation: port remaining md files to rst and add swh-web modules description in developers doc

closes T800