Implementing an Image_Handler and Header-Styles

[LukyLuke]

To be able to use images in docx reports and also headers from markdown, I decided to made these few simple changes.
To be able to use it also from DFIR-IRIS, I will also create a pullrequest there.

HTML-Tags in Links

Some people use HTML-Tags in link descriptions for example to add an Icon or emphasize something. This produces then a corrupt document.xml:

<w:r><w:t xml:space="preserve"><i class="icon icon_one" />Some text with a Link: </w:t></w:r>
<w:hyperlink r:id="rId13" w:tgtFrame="_blank"><w:r>
<w:t xml:space="preserve">[DS] siesta.jpg</w:t></w:r></w:hyperlink>

Maybe this is elsewhere the case too 🤔

Header Styles

We use a lot of markdown in our reports and therefore also headers, which where just stripped of till now.
I extended the styles with header1 to header5 and the DocxRenderer to use it as all other tags.

Image-Handler

Since DFIR-IRIS can handle Datastore-Images we also need them in our Reports. Therefore I have implemented an image_handler based on the PictureGlobal which can now handle local and http(s) images.
It downloads all the images and stores them in a subfolder of the generating report and adds them via the already implemented logic.

There is a inconvenience in docx.image.tiff class which also parses EXIF information from JPEG files. In case there is an unreadable or unknown resolution tag, the image cannot be added. I have not spotted this errors with PNGs. Because this costed me quite some time to figure out, i added a little better log and error message.
Open issue: python-openxml/python-docx#1124

Thanks for your work!
Lukas