* Remove deprecated PanicXXX functions from codebase
As per discussion over
[here](https://github.com/tendermint/tendermint/pull/3456#discussion_r278423492),
we need to remove these `PanicXXX` functions and eliminate our
dependence on them. In this PR, each and every `PanicXXX` function call
is replaced with a simple `panic` call.
* add a changelog entry
* crypto: revert to mainline Go crypto lib
We used to use a fork for a modified bcrypt so we could pass our own
randomness but this was largely unecessary, unused, and a burden.
So now we just use the mainline Go crypto lib.
* changelog
* fix tests
* version and changelog
