Alert user of invalid characters in /login, /signup, and /usersettings routes

[santosderek]

What would you like to add? Add a try and catch block to deal with the invalid characters exception when passing in invalid characters.

Describe the solution you'd like (If needed)

• [x] Add try, except blocks to /login, /signup, and /usersettings routes.
• [x] Exception must render error page to the user prompting them that invalid characters were used.
  • Should be similar to the other error prompts. Pass in a boolean to see if it exists and use jinja to render the error to the page.
• [x] Add unit tests to make sure that these errors are shown to the user.