Change Incorrect Sign-In Message

[mattbaseball]

Is your feature request related to a problem? Please describe.
The message given after an inaccurate login attempt is too complex. Consider simplifying the word choice to something like "These sign-in details do not match our records."... Something that will make more sense for a younger or less intelligent person.

[mattbaseball]

Also it'd be nice if you change the error message that occurs for a password change on an account that does not exist. (Although perhaps it is the same string anyways considering the current message is the same as the inaccurate login attempt.)