mainWindow's windowLevel should not be changed #48
Description
Changing the main window's windowLevel will cause some unexpected issues, such as using the library with Intercom: https://github.com/intercom/intercom-ios because the Intercom window is using windowLevel = 0.1 or some other values.
This library should use a value less than 0 to be the windowLevel for it's private passcodeLockWindow, and never change the windowLevel of the main window.
When presenting the passcodeLockWindow, it's window level can be a bigger number (such UIWindowLevelStatusBar - 1), but once it's dismissed, it should be set back to a number less than UIWindowLevelNormal.