* add custom css account property + db func to fetch
* allow account to get/set custom css
* serve custom css for an account
* go fmt
* use monospace for customcss, add link
* add custom css to account cache
* fix broken field
* add custom css docs to user guide
* add `accounts-allow-custom-css` config flag
* add allow custom css to /api/v1/instance response
* only show/set custom css if allowed to do so
* only set/serve custom account css if enabled
* update swagger docs
* chain promise
* make bool a bit clearer
* use cache for GetAccountCustomCSSByUsername
* move caption sanitization -> sanitize.go
* use sanitizeplaintext rather than removehtml
* rename sanitizecaption to sanitizeplaintext
* avoid removing html twice from statuses
* unexport remoteHTML
it's no longer used outside the text package so this
makes it less confusing
* test instance PATCH
