Consider being more explicit about what a "design" is

@mnearents suggests in !72 (comment 434822677):

should "Designs" be "Frames" since that's the Figma terminology and in GitLab we may change "Designs" to something else in the future?

The Figma plugin allows Figma Frames and Components to be uploaded, but we refer to them generally as "Designs" throughout the plugin. This issue is to consider making this more explicit.