dapp: Fix non-informative error message on SDK's wrapped errors

[andrevmatos]

Thank you for submitting this pull request :)

Fixes #1756

Short description
Wrapping errors as previously done on the RaidenService doesn't work, since passing Error objects to an Error constructur gets it serialized as unhelpful "[object Object]" string.
This fixes the error by exposing the original instance, as expected by ErrorMessage.vue component. If it's a known error, expected message is shown. Otherwise, the much more informative original message is shown.

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. Try to trigger the bug, as described

[codecov]

Codecov Report

Merging #1765 into master will decrease coverage by 0.00%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##           master    #1765      +/-   ##
==========================================
- Coverage   95.30%   95.29%   -0.01%     
==========================================
  Files         148      148              
  Lines        5328     5318      -10     
  Branches     1022      964      -58     
==========================================
- Hits         5078     5068      -10     
  Misses        203      203              
  Partials       47       47              

Flag	Coverage Δ
#dapp	91.43% <85.71%> (-0.06%)	⬇️
#sdk	96.85% <ø> (ø)

Impacted Files	Coverage Δ
raiden-dapp/src/services/raiden-service.ts	88.11% <85.71%> (-0.78%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 300a654...5b7ca2e. Read the comment docs.

[kelsos]

Lovely, thank you for doing this. Now that we have proper errors it makes sense to remove the unneeded wrapping.