Improve caching support for remote development

[PKief]

As mentioned in an issue at the VS Code Remote Development extension repository, there's an issue with recognizing changes in an extension file if the extension itself is flagged as pure "ui" extension. This affects the Material Icon Theme so far, that a change inside of the SVG files, as it is required for changing the color, opacity or saturation of the icons, is not recognized by the Remote Development extension.

So it is planned to work around this issue by updating the file names, if changes on the SVG code are necessary. That means that a change of the folder color will affect the default folder and workspace icon. If the opacity or the saturation is changed, it will affect all icon files (i.e. folder, file and workspace icons). The suggested idea is to encode the icon changes into the file name, e.g. folder-00ff00.svg.