Improve notification spam filter code.

- Follow coding style guidelines
- Replace dialog shown on click by adding the relevant information and
  the delete button to the item itself
- Minor layout tweaks
- Make the empty view more descriptive
- Add license headers

Change-Id: Ic685364087d6a093fdbb6a143a9c6ed78596b62b
(cherry picked from commit 1fbc15f1a4e992edc5c5b1ce541f42180abda3b8)
Automatic translation import

Change-Id: I1f9fc1e3a15c77fd725c3cae8ab619199cdfe04a

Conflicts:
	res/values-de/cm_strings.xml

(cherry picked from commit ac9f1bcdb857ea874d8ea56d200cdfe74b9da156)