[CritFix] Introduce raw content to text parts

[CritFix] Introduce raw content to text parts

Previously we had the following types of text content:

- `orig`: MIME *decoded* content
- `content`: same as `orig` but converted to utf8 and without HTML tags
- `stripped`: same as `content` but without newlines

Now we add `raw`:

- `raw`: raw mime content as it was in an original message

This also fixes R_BAD_CTE_7BIT rule