[feature/editor-code-tabs] Correctly count indentation on first line

Correctly count indentation on first line of code tag

PHPBB3-11557
[feature/editor-code-tabs] Apply code editor to everything

Move code editor from prosilver to assets
Apply code editor to subsilver2
Apply code editor to ACP elements where bbcode is allowed

PHPBB3-11557
[feature/editor-code-tabs] Check for browser support in function

Check for browser support and valid textarea in function instead of
before applying function.

PHPBB3-11557
[feature/editor-code-tabs] Make inTag function reusable

Change inTag function to reusable JS function that can check
for any BBCode

PHPBB3-11557
Merge remote-tracking branch 'remotes/cyberalien/feature/editor-code-tabs' into develop

# By Vjacheslav Trushkin
# Via Vjacheslav Trushkin
* remotes/cyberalien/feature/editor-code-tabs:
  [feature/editor-code-tabs] Make inTag function reusable
  [feature/editor-code-tabs] Check for browser support in function
  [feature/editor-code-tabs] Apply code editor to everything
  [feature/editor-code-tabs] Correctly count indentation on first line