Remember the email address for anonymous users

[NathanSudell]

Is your feature request related to a problem? Please describe.

• In my application sign in is optional, so I do not necessarily know the email address of a user
• When a user provides feedback they enter their email address in the Wiredash form
• If the same user wants to provide feedback again they have to enter their email address again
• Users have reported to me that this is frustrating and prevents them sending more feedback as they don't want to keep typing their email

Describe the solution you'd like

• Remember the previously used email address locally and use it again next time
• If an email address is set with setUserProperties it should override the previously stored value (as the user now logged in, we should use the same address they are logged in with)

Describe alternatives you've considered

• To retrieve the email address from Wiredash SDK and store it myself, but I could not find a way to do this

Additional context
n/a