Allow players to create reminder events for future dates

[Alexencandar]

Stellaris is pretty good about providing notices to players, but some things can be forgotten about still. For example, say you can't change your civics for 15 years because it is on cooldown and want to so as soon as possible, I suggest the ability for players to effectively create events, allowing a popup message at some future date, set by the player it would be also useful to allow players to track goals (ie have 10 colonies by 2220, trade network by 2030, etc.)