Assertion template enhancements

[agubler]

Type: feature

The following has been addressed in the PR:

• All code has been formatted with prettier as per the readme code style guidelines
• Unit or Functional tests are included in the PR

Description:

Refines the assertion template API, providing additional helper APIs and changes one API to clarify the functionality.

Adds primitive for ignoring widgets during the assertion, useful for lists where there is no need to assert every single item.

Assertion Template Enhancements

API's changed:

replace -> replaceChildren

(this #247 (comment) came back to haunt me*)

*Actually @matt-gadd 😄

API's added:

replace
remove
setProperties
getProperties

New Assertion Template primitive:

Ignore

Supersedes #314 fixing the conflicts and unit tests on IE