Use logger for messaging

[sheljohn]

• Remove +verb/ submodule, in favour of using the dk.logger.Logger implementation.
• Default logger should be created at startup.
• Additional function dk.logger.level to simplify level control.
• Alias method Logger:setFile, more explicit than open.
• Implement static class dk.logger.test to be called by assert/reject in order to redirect assertions to different channels.
• Remove static method callerInfo from Logger, and move it to separate dk.logger.chan instead (taking stack depth argument), which returns a struct with channel ID and caller string.
• Update Logger:write to take a channel as first input, and exclude empty caller from log line.
• Implement function dk.log, taking a channel as first input (or creating a default one if formatted message is passed directly), with a persistent instance of the default logger.

funciton log(varargin)
    persistent..

    args = varargin;
    if nargin  > 1
        v = args{1};
        if isstruct(v)
            chan = v;
            args = varargin(2:end);
        elseif ismember(v,{'w','e','...'})
            chan = dk.logger.chan( v, 4 );
            args = varargin(2:end);
        else
            chan = dk.logger.chan( 'i', 4 );
        end
    end
    L.write( chan, args{:} );
end

• Refactor functions dk.warn/info to call dk.log
• Remove ..if methods from Logger, in favour of directed assertions.
• Replace calls to dk.wassert/wreject with calls to assert with specified channels.