More verbose output for modules/controlpanel.cpp's DelNetwork / AddNetwork commands (updated)

Refer to previous pull request at https://github.com/znc/znc/pull/284 for a larger history of this pull request.

Cloned information:

I made a few minor modifications to controlpanel.cpp which increases verbosity of output (which is good for administrators).

For example:
Command: AddNetwork TestUser TestNetwork
Old Output: Network added [TestNetwork]
New Output: Network [TestNetwork] added for user [TestUser].

Command: DelNetwork TestUser TestNetwork
Old Output: Network deleted [TestNetwork]
New Output: Network [TestNetwork] deleted for user [TestUser].

The difference from the prior pull request is the third commit, which adds [ ] around usernames in the output.