Fix scaling and limits for Mastodon and Pleroma/Akkoma

[floogulinc]

• The max width and height are now calculated based on the maximum number of pixels provided by the instance and the aspect ratio of the file.
• max post length is now set by the max characters setting from the instance.
• Adds support for a max filesize and max post length from Pleroma and Akkoma instances.
• The chunk size is now determined by the max media attachments setting from Mastodon and Pleroma instances
• Updates the accepted filetypes based on what standard Mastodon supports. Ideally this would be from the list of mime types provided by the instance though.

[leaftail1880]

dont forget about npm run codestyle

[floogulinc]

Ah sorry about that, I've done that now.