Deploy token contract

[paulbellamy]

Fixes #81

Adds 2 new subcommands:

• $ soroban-cli token create --name "Example Token" --symbol "EXT" --decimal 7 --admin "G...5"
  Deploys a token smart contract for a new soroban token.

• $ soroban-cli token wrap --asset "USDC:G...5"
  Deploys the smart contract wrapper for an existing Stellar classic asset.

TODO

• Support deploying the token contracts to a remote soroban-rpc server
  • If we are doing the soroban-cli sandbox/remote distinction, these subcommands should probably be nested under that
• fix type conversion error with latest rs-soroban-env and rs-soroban-sdk
• Support actually invoking the deployed contracts in the sandbox
  • Moved to new issue: CLI: Invoke and serve should be able to call token contract methods #172
• Decide about renaming the subcommands
• Figure out how to test this
• update soroban-example-dapp: Use new soroban-cli token create subcommand soroban-example-dapp#20
  • One issue here, is that because CLI: Invoke and serve should be able to call token contract methods #172 is not done yet,it doesn't actually work... :/