Fix rng captcha generation error. Couldnt cherry-pick 0c2e99a9 because I decided to accidentally include an unrelated change

Set now non-default defParamCharset: "utf8" busboy option to correctly handle encoding of filenames that need utf8

v0.7.1

Closes #466, #464, #461, and #458

See merge request fatchan/jschan!254

Update CHANGELOG

When strict mime validation is enabled, actually tell the user what the server thinks the mime is in the mismatch error message.
note: only for making posts (for now), pending a refactor of some checks that are shared and duplicated between other file upload models e.g. banners/asset

Cleanup the captcha generators a bit, add comments, refactor duplicate getting distortions code to separate file.

Fix eslint no-unused-vars breaking express.use for error handler (needs 4 arguments in functio nsignature)

Catch obscure error that doesnt really break anything (more motivation to replace dogshit file mupload middleware

small fixups to the advanced sections
remove useless separators
add small section about getting help and smart questions
move advanced to collapsible section

update README
fluff up the features, referencing the new image

Fix static versioning string in gulp generate-favicon task that would cause issues with icons updating

redirected to a page that gives 403 because of no permission. instead redirect them anyway
-Add a ton of comments and do some small cleanup to improve maintaining forms.js

update CHANGELOG

re: the captcha one, roundrobin = too fast expiring, sampling expireAfter $gte some time = possible to not get returned a captcha. so stucking with random. been working fine.

1. because its only updated per hour, bump date is almost useless
2. hot threads are only for past 7 days so it it a better way to tell most replied vs most recent