Add new behavior to notification

[HeZiGang]

1. Add new behaver notification layer, freeze the layer when mouseover.
2. Fix lint issues.

[coveralls]

Coverage remained the same at 98.039% when pulling fa7697d on HeZiGang:master into 7568c4e on react-component:master.

[afc163]

You can try add test case for this feature.

[afc163]

[afc163]

And add a option for it, like we discussed in ant-design/ant-design#7513

[HeZiGang]

@afc163 , I saw that @benjycui said don't need add a new option for it and make the new feature as the default behave. so, i remove the additional option from source code.

anyway, I can try to add some test case for it.

[coveralls]

Coverage remained the same at 98.039% when pulling 2fdab2e on HeZiGang:master into 7568c4e on react-component:master.

[coveralls]

Coverage remained the same at 98.039% when pulling 2943094 on HeZiGang:master into 7568c4e on react-component:master.

[coveralls]

Coverage remained the same at 98.039% when pulling aec1233 on HeZiGang:master into 7568c4e on react-component:master.

[coveralls]

Coverage increased (+2.0%) to 100.0% when pulling efd62c4 on HeZiGang:master into 7568c4e on react-component:master.

[benjycui]

And add a option for it, like we discussed in ant-design/ant-design#7513

I think it is OK to be the default behavior of rc-notification.

[afc163]

Could be a little wired for message: http://ant.design/components/message/

[benjycui]

But if I put cursor on a message/notification, this means that I am reading the message, and it had better not disappear..