Merge pull request #2811 from Elberet/fix-bbcode-blocks

FIX: BBCode blocks parser no longer mangles JsonML arrays
FIX: while header drop down is dropped, header is in front
FIX: 404 if we try to navigate to a non-existant page
lower band check as well
FEATURE: Enable topic entrance on mobile
use && instead of and
FIX: `undefined` label on Top dropdown on mobile
FEATURE: staff option to unhide a post
fix broken build
FIX: Allow BBCode images within BBCode links
FEATURE: Add Archive Topics to Bulk actions

Add the ability to archive topics in bulk
https://meta.discourse.org/t/archive-topics-via-bulk/20302
Merge pull request #2814 from cpradio/add-bulk-archive-option

FEATURE: Add Archive Topics to Bulk actions
add a plugin outlet under avatars beside posts
FIX: j/k place tab focus accordingly so tab will go to the first linked item in the selected post/row

Allow tabbing to continue from the selected post/topic when using the j/k keyboard shortcuts
https://meta.discourse.org/t/when-a-post-is-selected-tab-should-take-you-to-the-first-link/16212
improve HTML plain text email error copy
FIX: Allow proper escaping of bold and italics markdown, even when
nested.
Merge pull request #2815 from cpradio/tab-to-first-link-on-post-when-using-keyboard

FIX: j/k place tab focus accordingly so tab will go to the first linked ...
FIX: allow API to create users when invite_only is true
FIX: send content length with backups
improve debuggability of code