config: create WebLetter.Config class

-has two published attributes; serverUrl, the action attribute,
 and method, the method attribute of the form
-not an optimal solution but far better than hardcoding
AddressToken: make street optional

Some addresses don't contain a street
remove unused token phone, add token footer
don't remove tokens from token array if in deregisterToken()
tokens: adapt to new token naming convention

-use opt-keyword instead of opt-token-keyword
-subtokens: don't add '-' (e.g. token-fromstreet instead of
token-from-street)
BooleanToken: use opt-token functionality

a BooleanToken does the same thing as an optional token, simply use the
optional token functionality to avoid duplication
Token: only change the enabled flag on input if input is a available
main app: remove isOptional flag from footer, rename logo