Consolidate multiple related notifications on the notification bar

**Issue by [brianschamel](https://github.com/brianschamel)**
_Thursday Mar 23, 2017 at 20:57 GMT_
_Originally opened as https://github.com/CQUI-Org/cqui/issues/420_

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This'd mainly be for DoWs, making peace, and city-state quests, as they are the ones that get stacked often.

Basically, instead of 9 different notifications for the start of a war between two civs with several suzerains each, combine the text from all into a list on a single notification.

However, with this system, it might be difficult to pick out the actual civs from among of city states,
to which I have 2 possible solutions:
1) Color code the cities, with different colors for you + your joint war partner (if you have one) (1 color), either of your CS's (2 colors), the enemy civs (3 colors), and their CS's (4 colors)
2) Instead, replace the notification text with "Russia (+3 city states ) has declared war/made peace with Arabia (+2 city states).

The issue does not name files, tests, or an entry point. Start by locating the notification-bar implementation and the existing declarations-of-war, peace, and city-state quest notifications; done means related notifications are consolidated into one readable notification without losing the involved civilizations and city states.

Written by the indexing model from the issue text.