Merges the keybase and Ledger code from go-crypto (which is no more) into the SDK
Adds support for Ledger into gaiacli
Cherry-picks updated error handling from #1158
* types/int: Switch Int, Uint to use pointers internally
This reduces the amount of pointer refs & derefs.
* Fix nil pointers on unmarshalling amino
* Fix elusive bug in marshalling with unitialized big int
* Remove debug code
* Switch big.rat to use pointers internally