Add tests for transactionPollingTimeout

[cgewecke]

Description

#3513

Adds some tests to verify the transactionPollingTimeout threshold is configurable for both web3.eth and contract methods and works as expected with geth interval mining.

Adds examples for the method configuration settings to the docs. In #3513 there was uncertainty about how the polling limit should be set since it seemed like it's not working.

(DRAFT: am requesting @miohtama for further review here because these (unsuccessfully) try to reproduce the config failure reported in #3513)

Type of change

• Tests

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.
• I ran npm run test:cov and my test cases cover all the lines and branches of the added code.
• I ran npm run build-all and tested the resulting files from dist folder in a browser.
• I have updated the CHANGELOG.md file in the root folder.
• I have tested my code on the live network.

[coveralls]

Coverage increased (+0.09%) to 89.732% when pulling 159cd79 on issue/3513 into a434ce1 on 1.x.

[ryanio]

Lgtm!