Fix per channel event monitoring and past events fetching

[andrevmatos]

Fixes #1434

Short description
Refactors the channel monitoring logic, which became more complex than it should. With little logs to investigate, and after some real life observation of some events being lost in very specific cases, this became the main target for thsi issue.
I did test by opening ~9 channels with hub, and this issue was not experienced.

Definition of Done

• Steps to manually test the change have been documented
• Acceptance criteria are met
• Change has been manually tested by the reviewer (dApp)

Steps to manually test the change (dApp)

1. Open and close a lot of channels with other nodes, with deposits, and check if any event is lost in the process
2. It helps by reducing the default timeouts. It was discovered that hub's raiden-py still accepts transfers with channels at { settleTimeout: 60 } (passed directly to Raiden.openChannel method), which is a huge improvement on waiting time over default=500.

[codecov]

Codecov Report

Merging #1475 into master will decrease coverage by 0.14%.
The diff coverage is 96.55%.

@@            Coverage Diff             @@
##           master    #1475      +/-   ##
==========================================
- Coverage   96.12%   95.98%   -0.15%     
==========================================
  Files         130      130              
  Lines        4798     4829      +31     
  Branches      963      969       +6     
==========================================
+ Hits         4612     4635      +23     
- Misses        139      148       +9     
+ Partials       47       46       -1     

Flag	Coverage Δ
#dapp	91.56% <ø> (ø)
#sdk	97.61% <96.55%> (-0.21%)	⬇️
#sdk_integration	?

Impacted Files	Coverage Δ
raiden-ts/src/utils/error.ts	98.68% <ø> (-0.02%)	⬇️
raiden-ts/src/transport/epics.ts	97.15% <80.00%> (-0.79%)	⬇️
raiden-ts/src/channels/epics.ts	98.95% <100.00%> (+0.37%)	⬆️
raiden-ts/src/channels/reducer.ts	98.78% <100.00%> (+0.04%)	⬆️
raiden-ts/src/channels/types.ts	100.00% <100.00%> (ø)
raiden-ts/src/channels/utils.ts	100.00% <100.00%> (ø)
raiden-ts/src/raiden.ts	94.05% <100.00%> (-0.27%)	⬇️
raiden-ts/src/services/epics.ts	99.07% <100.00%> (-0.03%)	⬇️
raiden-ts/src/transfers/epics/locked.ts	98.20% <100.00%> (-0.02%)	⬇️
raiden-ts/src/polyfills.ts	85.71% <0.00%> (-14.29%)	⬇️
... and 2 more

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[nephix]

Opened 5 channels with the hub and the issue didn't occur