Adds the possibility to define a custom registry for the ENS module

[nivida]

Description

This PR does extend the ENS module with the registryAddress property to define a custom registry and to store an already detected registry address. By side of the improvement of a stored registry address did I also improve the anyways changed checkNetwork method to only check the sync state of the node if at least an hour is gone. This because otherwise, it doesn't make sense to check it.

Fixes #3010

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• I have selected the correct base branch.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• Any dependent changes have been merged and published in downstream modules.
• I ran npm run dtslint with success and extended the tests and types if necessary.
• I ran npm run test:unit with success and extended the tests if necessary.
• I ran npm run build-all and tested the resulting file/'s from dist folder in a browser.
• I have updated the CHANGELOG.md file in the root folder.
• I have tested my code on a local test network.

[coveralls]

Coverage increased (+0.06%) to 85.424% when pulling 69001c7 on issue/3010 into 513116f on 1.x.

[cgewecke]

This looks perfect to me, awesome. 💯

I left one question and a couple small rewording suggestions for the docs.

[nivida]

@cgewecke Thanks for your review! I've fixed the commented typos with 69001c7