Merge the develop branch to the master branch, preparation to v5.2.0

[akolotov]

This update provides the following new functionalities and fixes:

• [Improvement] Use uint256[N] instead of uint256[] (Use uint256[N] instead of uint256[] #447)
• [Improvement] Use permittable ERC677 token by default for AMB mediators (Use permittable ERC677 token by default for AMB mediators #451), closes Support metatransactions using GSN & ERC-2612 permit #450
• [Fix] Bump npm-registry-fetch from 4.0.0 to 4.0.5 (Bump npm-registry-fetch from 4.0.0 to 4.0.5 #446)
• [Fix] Bump lodash from 4.17.15 to 4.17.19 in /deploy (Bump lodash from 4.17.15 to 4.17.19 in /deploy #449)
• [Fix] Support negative decimal shift (Support negative decimal shift #448)

In order to bump the version the following PR was also merged:

• [Other] Bump version to 5.2.0 before merging to master (Bump version to 5.2.0 before merging to master #453)