feat(gov): adapt voting period to proposal content

[tbruyelle]

Summary

We want the voting period of proposals to be 1 year, in order to allow any participant to vote, even for late-comers.

Problem Definition

This is problematic for upgrade or params proposals, they should have a shorter voting period.

Proposal

Adapt the voting period according to proposal content.

• text proposal voting period : 1 year
• params change proposal voting period : 2 weeks
• upgrade proposal voting period: 4 weeks

[tbruyelle]

Since the fork of the gov module excluded gov/types, it's not possible to update the VotingParams to include other voting periods. The solution may be

• add a VotingParams2 with different voting periods
• Set the voting period to 2 weeks for all proposals, and when the voting period ends, extend it to another 2 weeks for params changes, or 1 year-2 weeks for text proposals (at this stage, it's probably better to never end the voting period for text proposals).