[ticket/13025] Add button template events

PHPBB3-13025
[ticket/13025] rc4 -> rc5

PHPBB3-13025
[ticket/13025] Make RC uppercase

PHPBB3-13025
[ticket/13025] Correct events in subsilver2 viewforum_body

PHPBB3-13025
Merge pull request #3019 from Senky/ticket/13025

[ticket/13025] Add template events for buttons on viewforum and viewtopic