[ticket/12857] Add template events breadcrumbs_before/after

PHPBB3-12857
[ticket/12857] Add missing template events breadcrumb_prepend

To insert links after site-home

PHPBB3-12857
[ticket/12887] Fix Typo: offest -> offset

PHPBB3-12887
[ticket/12857] Clarify events.md on difference between PS and SS2 breadcrumbs

PHPBB3-12857
[ticket/12857] Add header/footer distinction for subsilver2 events

PHPBB3-12857
Merge remote-tracking branch 'paybas/ticket/12857' into develop-ascraeus
Merge pull request #2773 from bantu/ticket/12887

[ticket/12887] Fix Typo: offest -> offset
[ticket/12881] Checks earlier if server-side topic marking is enabled

PHPBB3-12881
[ticket/12892] Do not set S_NUM_ROWS when adding a row to a template loop

We do not set S_NUM_ROWS while adding a row, to reduce the complexity
If we would set it on adding, each subsequent adding would cause
n modifications, resulting in a O(n!) complexity, rather then O(n)

PHPBB3-12892
Merge pull request #2779 from nickvergessen/ticket/12892

[ticket/12892] Do not set S_NUM_ROWS when adding a row to a template loop

* nickvergessen/ticket/12892:
  [ticket/12892] Do not set S_NUM_ROWS when adding a row to a template loop
Merge pull request #2777 from Nicofuma/ticket/12881

[ticket/12881] Debug error - Undefined index: mark_time

* Nicofuma/ticket/12881:
  [ticket/12881] Checks earlier if server-side topic marking is enabled