Issue #49707 by vprocessor, gargsuchi, DuaelFr, andypost, ilya.no, jonathanshaw, tangent, alexpott, Anybody: Move comment fragment identifier to the comment container

- Patch #17303 by tangent: moved the session settings into /sites/default/settings.php so that subsites can have better control over them. One of the advantages of the site specific settings.php file is that it will never get overwritten during upgrades and having these settings here should prove to be more friendly.

- Patch #14710 by tangent: only show post button if preview is optional or if we are in preview mode.  We show the post button in preview mode even if there are form errors so that optional form elements (e.g., captcha) can be updated in preview mode.