Dashboard: better UX for app tiles

give more information to users about the apps on the dashboard, so they have a better idea of what to expect when clicking on "launch app"

includes

• complete descriptions and tutorials for each app moved to #145 (closed)
• show content excerpt for each app on tile
• create way to activate modal with extra information
• style modal

To make it more apparent to users what they have and how that changed recently, we'd like to

• Show the current Stackspin version.
• Show the version of apps in the Apps module.
• Show some sort of notification when a Stackspin release is imminent or has already been deployed, pointing to or showing the release notes.

To achieve this, we will:

• create a sysInfo API end point that provides us with this information
• build a Redux service in frontend that ingests the API, adds it to app state, and exposes it as a resource acros the app
• build components and UI for the dashboard that use that API