Add a 1.3.0 -> 1.4.1 migration contract

[mmv08]

This PR:

• Adds a migration contract from 1.3.0 to 1.4.1 with migrate and migrateL2 methods. The contract inherits from the SafeStorage library and changes the singleton address to one of the hardcoded addresses (l1 or l2). It also calls safe's setFallbackHandler method during the migration. The motivation for adding the fallback handler upgrade is to upgrade a Safe in one transaction without using nested delegate calls.
• Tackles #638 for 1.4.1

Review notes:

• Hardcoded addresses are taken from https://github.com/safe-global/safe-contracts/blob/bf943f80fec5ac647159d26161446ac5d716a294/CHANGELOG.md#version-141
• I had a weird bug with prettier, and had to do the infamous rm -rf node_moduless & rm -rf package-lock.json && npm i, hence the updated lockfile

Possible improvements:

• Should it check that the contracts at hardcoded addresses are deployed?

[coveralls]

Pull Request Test Coverage Report for Build 6049647957

• 17 of 17 (100.0%) changed or added relevant lines in 1 file are covered.
• 7 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-1.2%) to 91.566%

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Files with Coverage Reduction	New Missed Lines	%
contracts/SafeL2.sol	7	0.0%
<!--	Total:	7		-->

Totals
Change from base Build 6047382307:	-1.2%
Covered Lines:	330
Relevant Lines:	357

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💛 - Coveralls