example-dapp: update per token interface changes

[tsachiherman]

What ?

Update example dapp to use the updated token interface.

Epic

stellar/stellar-cli#519

[2opremio]

This ticket requires updating https://github.com/stellar/soroban-example-dapp/blob/main/contracts/crowdfund/src/lib.rs with the new token spec (and updating the corresponding function calls to their new names)

[2opremio]

And it may also:

1. require bumping the Rust SDK to an unreleased version (with the new token contract changes and a new soroban_sdk::contractimport)
2. bump core/QuickStart to a newer version supporting the new token interface

For all the above, we can use stellar/stellar-cli#611 as a reference

[sreuland]

closing as done, updates were merged in #105