[FEATURE] - User-Friendly Home / Dashboard

[JSv4]

Create a new landing page for users that provides some top-level steps - e.g. total docs, total corpuses, total configured extractors, etc. - that is also a place to suggest actions for users. E.g. if a user has an empty account with no data, gently offer to help them create a corpus or upload and analyze a document. Maybe make the single document analysis workflow discussed in #152 available on this page via a simple file dropzone.