Theme-defined icons support (including SVG, font-based)

[kuzhelov]

Feature Request

Problem description

Currently it is impossible for theme author to define set of icons that could be rendered by Icon component. Specifically, if theme author would like to introduce icon foo and consume it in the following way with her theme being applied, currently there is no way to achieve that

<Icon name='foo'>

Proposed solution

Here is the plan we see to address this issue

• introduce mechanics of consuming icons from theme
  • now is introduced for SVGs (feat(icons): add support for styling SVG icons #183), should be generalised for font-based icons as well (feat(theme): add font icons support for themes #243)
• resolve aspects related to sizing (it should be possible to pixel-perfectly customize size of the icon)
• support icon's outline/filled variants
• support changing look of the icon on hover state

[kuzhelov]

closing as all the mentioned steps are made :)