Update comicbook file extensions

cb7, cba, cbr, cbt and cbz all refer to different types of digital
comicbooks. The last letter of the extension indicates the compression
algorithm that was used: 7zip, arc, rar, tar or zip.

All these filetypes used to have the `application/x-cbr` MIME type
assigned to them. However, that has since been deprecated and was
replaced with

- `application/vnd.comicbook-rar` for rar compressed files and
- `application/vnd.comicbook+zip` for rar compressed files.

Only these two are officially listed by IANA

https://www.iana.org/assignments/media-types/application/vnd.comicbook+zip

. cbr and cbz are by far the most common file extensions for comicbooks.

There's no official MIME type for cb7, cba or cbt files. However, with
rar being a proprietary compression algorithm, FOSS applications will
often refuse to handle files that identify themselves as
`application/x-cbr`, so I decided to assign extension specific MIME
types to them. I've seen these being used by other applications,
specifically comic book readers.

I've read through the docs on iana.org, but haven't figured out why they
chose `-rar`, but `+zip`.

This fixes khellang#23.

src/MimeTypes/MimeTypes.NullableAttributes.cs.pp

@@ -140,11 +140,11 @@
                 { "cap", "application/vnd.tcpdump.pcap" },
                 { "car", "application/vnd.curl.car" },
                 { "cat", "application/vnd.ms-pki.seccat" },
-                { "cb7", "application/x-cbr" },
-                { "cba", "application/x-cbr" },
-                { "cbr", "application/x-cbr" },
-                { "cbt", "application/x-cbr" },
-                { "cbz", "application/x-cbr" },
+                { "cb7", "application/x-cb7" },
+                { "cba", "application/x-cba" },
+                { "cbr", "application/vnd.comicbook-rar" },
+                { "cbt", "application/x-cbt" },
+                { "cbz", "application/vnd.comicbook+zip" },
                 { "cc", "text/x-c" },
                 { "cco", "application/x-cocoa" },
                 { "cct", "application/x-director" },

src/MimeTypes/MimeTypes.cs.pp

@@ -140,11 +140,11 @@
                 { "cap", "application/vnd.tcpdump.pcap" },
                 { "car", "application/vnd.curl.car" },
                 { "cat", "application/vnd.ms-pki.seccat" },
-                { "cb7", "application/x-cbr" },
-                { "cba", "application/x-cbr" },
-                { "cbr", "application/x-cbr" },
-                { "cbt", "application/x-cbr" },
-                { "cbz", "application/x-cbr" },
+                { "cb7", "application/x-cb7" },
+                { "cba", "application/x-cba" },
+                { "cbr", "application/vnd.comicbook-rar" },
+                { "cbt", "application/x-cbt" },
+                { "cbz", "application/vnd.comicbook+zip" },
                 { "cc", "text/x-c" },
                 { "cco", "application/x-cocoa" },
                 { "cct", "application/x-director" },