Fix #1033 as well as other (potential) similar issues

Added type="button" (and type="submit" where applicable) to buttons to prevent <button> acting as a submit (which is default, thanks w3c), i.e. it would be "clicked" if enter is pressed.

Most notably - #1033 (closed) fixes OTP entry and recovery forms and fixes hitting "enter" in subject line input triggering the emoji picker.

Also did small change to EmojiReact button's classnames for consistency and tija's sake so it's easier to write userstyles for.