Inconsistent lower case names of HTMLEditor related files

[sb-relaxt-at]

Nearly all files related to HTMLEditor are using the lower case acronym "Html", e.g.:

• HtmlEditorConfig.php
• HtmlEditorSanitiser.php
• HtmlEditorField.php

From my point of view, adhering to the coding convention, they should use the upper case version (as in "HTMLText.php", etc.).

[tractorcow]

I think when we namespace all classes, it could be done as a part of that change.

See #4562

[tractorcow]

I really have no feeling either way. PHP classes are case insensitive, so it theoretically shouldn't hurt to rename them, although I think the config API might have some issues.