SecretStore: generating signatures (#5764)

* refactoring traits

* separate generation session

* generalized ClusterSessions

* signing session prototype

* full_signature_math_session

* consensus session prototype

* continue signing session

* continue signing session

* continue signing session

* continue signing session

* isolated consensus logic

* started work on signing test

* complete_gen_sign_session works

* consensus tests

* get rid of duplicated data in SigningSession

* TODOs in signing session

* fixing tests

* fixed last test

* signing session in http listener

* new key server tests

* fix after merge

* enabled warnings

* fixed possible race

* ignore previous jobs responses

* include sef node in consensus when confirmed

* fixed warning

* removed extra clones

* consensus_restarts_after_node_timeout

* encrypt signature before return

* return error text along with HTTP status

* fix for odd-of-N (share check fails + not equal to local sign)

* fixed t-of-N for odd t

* fixed test cases in complete_gen_sign_session

* fixed mistimed response reaction

* jobs draft

* DecryptionJob

* consensus session tets

* fixed decryption tests

* signing job implementation

* siginng_session using new consensus_session

* added license preambles

* same_consensus_group_returned_after_second_selection

* database upgrade v0 -> v1

* typo

* fixed grumbles