Changes and updates to message relaying, NV registry key/config separation, new prefixes

This change does a few things which I found useful for my installation:

* Relay channel msgs/notices/ACTIONs to other clients connected to this ZNC user/network
* Separate out the NV registry some more, prefixing keys with ``key ``
* Adding config options, prefixed with ``config ``, making the encrypted and decrypted (e)/(d) prefixes settable
* Change the default encrypted/decrypted prefixes to blue e or red d, depending on whether the message had to be decrypted or not

**PLEASE NOTE**
This does upgrade your key database, going through and adding ``key `` to the start of them. It **does not** delete your old prefix-less keys (the old style), so you can still just throw your master branch back on, but you would need to go through afterwards and delete a bunch of useless 'keys'

**I would very strongly recommend making a backup of your database before loading this, to make it simpler to revert back if necessary**