View groups

1. Switcher no more relies on FrameLayout.
2. You can have multiple error, empty or progress views being shown/hidden simultaneously
3. You need to remember to register with switcher every parent view you wan't to show/hide
4. Removed blur feature as it doesn't really belong here. If you're interested in it please create an issue and maybe I'll create separate lib for that.
5. Due to the changes some basic methods changed names. Readme got updated accordingly.