Live Content 1.5.4

• XF2.1 compatibility update

• Fix compatibility with some configurations of Apache webserver unexpectedly returning 304 (not modified) when polling for updates

• Ensure polling still continues after a 304

• Do not stop polling if a 304 error is returned
• Tweak caching headers, again

• Avoid race condition between adding an already existing post
• Fix tracking of last content to fetch
• Only signal stop polling when polling is no longer permitted to avoid false positives.
• Prevent caching from triggering false positives which stops polling

• Improve robustness of how the last post seen is tracked
• Do not scroll if the post is added above the viewport

• Fix session activity tracking returning 'managing account details' when polling for changes