encrypt targets/keys

@freshprince @mumixam

Here is the fixed version of what I originally submitted. It encrypts both targets and keys, and switches to core.weechat when loaded.

I'm hesitant to start using sec.conf after getting more familiar with it. The problem is that, if we encrypt a key or the blowfish keys in it, then weechat will prompt for a password to decrypt them regardless of whether or not fish.py is loaded.

However it would be easy to use them if that's not a concern. We could easily move the blowfish keys into sec.conf and then the user would be able to optionally encrypt them with `/secure passphrase MyPassphrase`

What are your thoughts? I'm going to create a branch to try this out in and then send another PR.

Also, @freshprince what did you mean about moving `/blowkey setpw` and `/blowkey unsetpw` into the "settings hook"? Do you mean the `config_init`?