Implement state upgrades and migration

[andrevmatos]

Fix #614
Part of #152

• A new submodule is implemented: src/migration/
• State migration functions are implemented as a default exported function in numbered version modules, like src/migration/0.ts, which must always take a state from version N-1 and migrate to state N.
• This function must then be imported on src/migration/index.ts, and put in a corresponding versioning entry in the migrations mapping object, and is applied with a migrateState function (as any/type-unsafe input & output)
• src/state/decodeRaidenState function then calls migrateState to apply the needed upgrades in order on the parsed state object, throwing if anything goes wrong in each step, and then validating/decoding the resulting data against current RaidenState schema, throwing if it fails as well
• 3rd argument of Raiden.create, which previously accepted localStorage xor state, now also supports both through an object in the format { storage; state? }, which can be used to upload a state, to be used instead of the stored one, while keeping localStorage setup (persistence).
• It fails if trying to load an old state on top of a newer one (determined through blockNumber), and manual state purging is required if one wants to force loading a state (backup) through it
• Migration is always applied to either stored or uploaded states, ensuring we can continue with previous state on new versions
• It applies only to state upgrades on the same contracts/blockchain/account. It doesn't help when network upgrades through a new contracts deployment.
• A set of JSON test files containing an example of minimum and full states for each version, always migrated, decoded & validated to current version, ensures present & future compliance and state upgradeability.

[codecov]

Codecov Report

Merging #1050 into master will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1050      +/-   ##
==========================================
+ Coverage   96.11%   96.14%   +0.02%     
==========================================
  Files          96       97       +1     
  Lines        3658     3681      +23     
  Branches      776      748      -28     
==========================================
+ Hits         3516     3539      +23     
  Misses         88       88              
  Partials       54       54              

Flag	Coverage Δ
#dapp	91.53% <ø> (ø)	⬆️
#sdk	98.01% <97.77%> (+0.01%)	⬆️

Impacted Files	Coverage Δ
raiden-ts/src/migration/0.ts	100.00% <0.00%> (ø)

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[kelsos]

lgtm 👍 thanks