Develop the fuction which enable Magteam to re-elect sequencers from Collators

[Acaishiba]

This function will allow Magsteam to have the capacity to elect the sequencers from Collators.

1. The election will completed at the beginning of each era (Synchronise with the election of Collators)
2. The candidates of sequencers are ordered by the re-staked value of them
3. The value of the re-staked token shouldn't be less than 2/3 of the average
4. The eligible candidates will be elected as the sequencers
   @wd30130