Consider using types that ensure ordering in elections-phragmen

[kianenigma]

As per noted here, after a number of bugs that were caused because of broken assumptions about the ordering of runners-up, it is worthy to consider using types that ensure order (i.e. SortedVec), at the cost of a bit less performance, to ensure veracity.

See the discussion here for more. #7384 (comment)

[xlc]

There are many other places should also use SortedVec such as the balances lock

[shawntabrizi]

Could also use a type for vec of maximum length, for things like strings, or other weight limit related stuff.