proposals: add tick height from proposals to blocks

[dshulyak]

• add highest known base tick height from activation that are referenced in the proposals to the block. this will be used later in the tortoise to prevent adversarial votes using ballot with lower tick heights
• when choosing valid block from multiple valid blocks use the lowest tick height. the idea is that the lower the tick height - the more time honest voters had to vote

[dshulyak]

bors merge

[bors[bot]]

Pull request successfully merged into develop.

Build succeeded:

• ci-stage2