Part 1:

While I reproduced #3686 I saw that the time to read the notification is to short (4 seconds).

Changes proposed in this pull request:

• if it is a 'bad' (=red) notification, than the time is doubled to disappear (= 8 seconds)
• if the user moves the mouse pointer over the notification, the timer stopps
• if the user's mouse pointer leaves the notification it will disappear after 1 second
• changed the onlick-event of the close icon to addEventListener

How to test the feature manually:

1. go to subscription management: page 'add a feed or category'
2. press the 'add' button of 'add a category' (leave the input empty!)
3. a read notification will appear
4. test the changes

Part 2

Before:
The text inside of the notification could be hidden behind the close button and the grey button could be invisible over the text. And the line-height is strange.

After:
No text anymore behind the close button.

While hovering the grey icon will become white

I checked all themes and improved it in some little cases (f.e. readable links)

Pull request checklist:

• clear commit messages
• code manually tested