Widgets don't need anymore a key `elements`
Remove all `elements` keys from all tests' widgets.
Update changelog
Update documentation. Remove key `elements` in widgets examples.
Correct documentation of `Widget` constructor and `extractElementsAndMethods` method
Rename `Methods` into `Actions` for consistency.

User documentation refers to widgets' methods as actions.
Add missing semicolon
Refactor timeout-prone Feature test
Remove `elements` sub-hash in widgets definition
Improve Widgets syntax

Fixes #80