Improve UX for dashboard app tiles

First commit; it was quite a challenge to get the local instance running properly. One of the changes I did is to expand the scope of docker-compose because it was only mapping the src directory to a container, which meant that all data outside it was super old.

• Right now the dashboard correctly pulls information from individual Markdown files for each app. The files are stored in frontend/public/markdown.
• I installed gray-matter to allow for parsing of frontmatter in markdown files. That way each file can hold descriptive data that we can use on the dashboard, like the excerpt.
• The dashboard tiles now also have a small question mark icon that opens a modal window. This window will hold all the information we think people might need when using apps. Stuff like what to do on first login, or whether the app has a "sign up with stackspin" or a "sign up with Oidc" button, etc. Not a lot of content, but enough to let people know what is expected.
• There is now a "status" dropdown that gives version and extra info about the instance
• added custom alerts for when an update is imminent and right after an update
• made the dashboard title more personal, with a sensible default fallback to email
• added the external app functionality to the UX based on previous work by @mart, rewriting it to use the API instead of the manual list
• tagged all apps as either "core" or "external." this tagging happens automatically based on API information
• created a separate custom folder in public to store custom logos and markdown files. There is also a default logo and a default markdown file as fallbacks in case the files aren't there and/or ready
• changed the "launch app" button to "login with stackspin" for external apps
• verified that all user configuration modals are only accessing API-pulled apps
• removed the manual apps list from system and code

Closes #142 (closed)