Made PreBodyTagFilter more robust, Fixes issues #341 (partially) and #442 (completely)

So that it will now detect and handle accordingly the following situations:
- only 1 </body> tag is present (will be prefixed with snippet if needed)
- multiple </body> tags are present(only last want will be prefixed with snippet it needed)
- no </body> tags are present
- detect non standard casing of </body> tags (</BODY>,</BoDy>...)