Update formatscaper according to identified requirements

During test runs, we saw that a "flat" assessment of endangerment status per file format ("endangered" vs. "safe") isn't enough. Even if a file format is at risk of becoming obsolete (or is already dead), this doesn't necessarily mean that a dataset containing such files is necessarily at risk (e.g. vim swap files likely just end up in the dataset accidentally and could be removed).

As such, we started following more of a risk management approach by evaluating the risk for each file, based on the probability of its format becoming obsolete, and the impact severity in case this file becomes uninterpretable.

tests/data/test_formats.yml

+- puid: x-fmt/111
+  name: Plain Text File
+  mime: text/plain
+  risk: 1
+- puid: x-fmt/263
+  name: ZIP Format
+  mime: application/zip
+  risk: 2
+- puid: UNKNOWN
+  name: null
+  mime: null
+  risk: 5
+- puid: fmt/818
+  name: YAML
+  mime: null
+  risk: 1
+- puid: fmt/938
+  name: Python Source Code File
+  mime: null
+  risk: 3
+- puid: fmt/1149
+  name: Markdown
+  mime: text/markdown
+  risk: 1
+- puid: fmt/43
+  name: JPEG File Interchange Format
+  mime: image/jpeg
+  risk: 1
+- puid: fmt/615
+  name: Gimp Image File Format
+  mime: null
+  risk: 3
+- puid: x-fmt/390
+  name: Exchangeable Image File Format (Compressed)
+  mime: image/jpeg
+  risk: 1
+- puid: fmt/12
+  name: Portable Network Graphics
+  mime: image/png
+  risk: 1
+- puid: fmt/1639
+  name: Adobe InDesign Document
+  mime: null
+  risk: 2
+- puid: fmt/13
+  name: Portable Network Graphics
+  mime: image/png
+  risk: 2
+- puid: fmt/11
+  name: Portable Network Graphics
+  mime: image/png
+  risk: 2
+- puid: fmt/276
+  name: Acrobat PDF 1.7 - Portable Document Format
+  mime: application/pdf
+  risk: 1
+- puid: fmt/215
+  name: Microsoft Powerpoint for Windows
+  mime: application/vnd.openxmlformats-officedocument.presentationml.presentation
+  risk: 2
+- puid: fmt/412
+  name: Microsoft Word for Windows
+  mime: application/vnd.openxmlformats-officedocument.wordprocessingml.document
+  risk: 2
+- puid: fmt/199
+  name: MPEG-4 Media File
+  mime: application/mp4
+  risk: 2
+- puid: x-fmt/391
+  name: Exchangeable Image File Format (Compressed)
+  mime: image/jpeg
+  risk: 1
+- puid: fmt/471
+  name: Hypertext Markup Language
+  mime: text/html
+  risk: 1
+- puid: fmt/92
+  name: Scalable Vector Graphics
+  mime: image/svg+xml
+  risk: 1
+- puid: fmt/4
+  name: Graphics Interchange Format
+  mime: image/gif
+  risk: 1
+- puid: x-fmt/224
+  name: Cascading Style Sheet
+  mime: text/css
+  risk: 1
+- puid: fmt/20
+  name: Acrobat PDF 1.6 - Portable Document Format
+  mime: application/pdf
+  risk: 1