feat: Event triggers

[UberWaffe]

Added event trigger for building caught fire
Added event trigger for building collapse poor maintenance

This allows for events to trigger their checks on events other than the start of a new game month.
Currently added trigger types include: Building catching fire, building being constructed, building deleted by player, etc.

Also adds the concept of 'context'.
For these new types of triggers, this is the type of building that is involved.

I.e. You can do things like fire off an event when the player places a specific type of building.
Or when a specific type of building (or even any type) catches fire.

Should support redoing the tutorials completely with events only.

[crudelios]

Great idea! I'll have a look when I have the time.

[crudelios]

Also, if you don't mind I'll just look into this after #1169 is merged.

[UberWaffe]

No problem, I'll rebase once #1169 is merged.

[UberWaffe]

@crudelios Rebased, incorporated the condition group and other changes, and tested.
Tested loading of old save games from before condition groups.
Tested loading of old scenarios from before condition groups.
Tested of saving and loading on new version for saves and scenarions.
Tested XML export and import.

[UberWaffe]

Rebased after c2c958b (Fix importing of malformed event xml files).

[crudelios]

Oops, new recent conflict in translation file! Can you fix so I check this please?

[UberWaffe]

@crudelios Rebased on latest

[crudelios]

@UberWaffe This needs a rebase again, and this time I promise I'll have a look.

[Sephirex95]

If you're able to resolve merge conflicts, I can review and merge - this is in line with the current goals for 4.5