Schedule validations/sanity checks

[jfly]

(cc-ing @viroulep for his thoughts. This might be redundant with some of his work in #3207, which I have not looked at yet)

Some people have brought up some schedule "validation" they'd like our schedule tool to do. This is a list of them:

• A Final can (timewise) be before a First round. This should be forbidden. -@Goosly in Events Tab #3169 (comment)
• ...?

[Goosly]

Similarly, FMC/MBLD attempts can start before the previous attempt has finished. This should be forbidden. Note that these attempts may be assigned to different rooms, so it should be checked across all rooms.

[c-goodyear]

The same round being added multiple times should be flagged for the user to know that it has been added multiple times. This can happen by design (bigBLD, seperate stages etc) but can also be a mistake from an organizer/Delegate who then fail to notice it has been appended to the schedule twice.

Currently there is a shading system in place on the round buttons for the schedule. Dark being yet to be appended, light have been appended. My suggestion would be to flag these in a color that is not blue, so it is obvious to those who unintentionally added a second instance of the same round.

[viroulep]

I've not put much thoughts into this yet, but given we should probably look into an "extensible" solution I'd suggest implementing an extra entry in the menu here:

Which would display the list of sanity checks which fail (with two versions of the icon: one if everything looks good, one with some red eye-catching thingy as soon as one sanity check fails).

[AlbertoPdRF]

If it's visible enough when a sanity check fails, that may be a good idea!