feat(core): optimize bundle size

[danielleroux]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (yarn build) was run locally and any changes were pushed
• Unit tests (yarn test) were run locally and passed
• Visual Regression Tests (yarn visual-regression) were run locally and passed
• Linting (npm lint) was run locally and passed

Pull request type

Please check the type of change your PR introduces:

• Bug fix
• Feature
• Refactoring (no functional changes, no API changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the new behavior?

• Replace all icons inside the lib with import style (no webfont files need for core anymore)
• Change import style of web components

When we have solved issue #138 we expect a further improvements regarding bundle size.

Testing

React starter project with basic-navigation, menu and a button

• (Left) @siemens/ix, @siemens/ix-react and @siemens/ix-icons with latest released version (1.6.x) results in a dist output of 2.2MB
• (Right) same setup and demo code (after the refactoring) results in a dist output of 756KB

Does this introduce a breaking change?

• Yes
• No