Fix: Make sure toolkit includes the theme css

[jackw]

Recent versions of worldmap panel have started printing out loading errors due to missing theme css. With the migration to toolkit the codebase needs to adopt the naming conventions set out by toolkit...

Theme-specific stylesheets
If you want to provide different stylesheets for dark/light theme, then create dark.[css|scss] and light.[css|scss] files in the src/styles directory of your plugin. grafana-toolkit generates theme-specific stylesheets that are stored in dist/styles directory.

In order for Grafana to pick up your theme stylesheets, you need to use loadPluginCss from @grafana/runtime package. Typically you would do that in the entry point of your plugin:

import { loadPluginCss } from '@grafana/runtime';

loadPluginCss({
dark: 'plugins//styles/dark.css',
light: 'plugins//styles/light.css',
});

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[briangann]

i'll need this in other plugins, looks great!