Add `ProxyAdmin` module to manage ERC-1967 data

[ItsNickBarry]

Mentioned in #292.

External setters are needed, but won't work for the Transparent proxies. Those contracts should still inherit the same internal functions, however.

Also need a "safe" module equivalent to SafeOwnable.

[ItsNickBarry]

To set the implementation or beacon, maybe setImplementationSource(address) could work in both cases.