fix(did-ethr-provider): allow initialization with chainId number

[mirceanis]

This allows numbers to be used for the network parameter of EthrDidProvider.

'did:ethr:421611': new EthrDIDProvider({
  network: 421611,
  // ...
}),

This is a small workaround until EthrDidControler API can be improved to accept more flexible configuration.
fixes #677

I also rearranged some of the imports in the integration tests for easier development.

[codecov]

Codecov Report

Merging #678 (1433c00) into next (88264db) will increase coverage by 11.47%.
The diff coverage is 74.48%.

@@             Coverage Diff             @@
##             next     #678       +/-   ##
===========================================
+ Coverage   67.58%   79.06%   +11.47%     
===========================================
  Files          62       78       +16     
  Lines        1530     2364      +834     
  Branches      247      415      +168     
===========================================
+ Hits         1034     1869      +835     
- Misses        400      493       +93     
+ Partials       96        2       -94