normalize log level before setting

[seanplwong]

Fix #660

[james-criscuolo]

Thank you for taking a look at this, it is very close to being mergeable. I have a small issue with this line: 8646cc6#diff-b45d4be906fc4401f1fd5133946b5250R178

We used to be able to set any string here, so if someone passed a custom connector with their own levels than I believe it would work. Now, if they were to pass that string, it would end up as undefined here.

The paths forward would either be:

1. Make the type passed in Levels | number
2. change the above line to set the string to what was passed if Levels[string] is undefined.

Choice 2 preserves behavior, so it should be the change made.

[seanplwong]

level used to be like this:

    level: {
      get: function() {return level; },
      set: function(value) {
        if (value >= 0 && value <=3) {
          level = value;
        } else if (value > 3) {
          level = 3;
        } else if (levels.hasOwnProperty(value)) {
          level = levels[value];
        } else {
          logger.error('invalid "level" parameter value: '+ JSON.stringify(value));
        }
      }
    },

So i think custom level is not handled previously as well, it will log an error.

And even after that, it will stubble upon LoggerFactory#genericLog()

  public genericLog(levelToLog: Levels, category: string, label: string | undefined, content: any): void {
    if (this.level >= levelToLog) {
      if (this.builtinEnabled) {
        this.print(console[Levels[levelToLog]], category, label, content);
      }

      if (this.connector) {
        this.connector(Levels[levelToLog], category, label, content);
      }
    }
  }

when this.level is string, it will return false no matter what and skip everything: 'anystring' < 1000 is false.
'1' < 3 will work tho.

[seanplwong]

but we could inverse the control here, just let connector decide what it wants to do.