This commit tackles two important problems with our contract code
- use of solana-sdk - I exile the code that relies on solana-sdk's
Keypair to a new solitaire-client crate that will conveniently handle
such client-only cases from now on
- Don't use `const-generics_defaults` - latest official release of
solana does not allow for using them and I don't find it practical to
install the experimental toolchain.
Change-Id: I3319db109de4ebcce9091e0284e756ce09264985
Stan Drozd