Updated the discover popup layout / style.
Style-fix
Changed discover layout into a grid to make it more readable.
Ditched the left-side tray.
Fixed the add to all cards bug.
Added 'true' flag to preserve the default channel broadcast / listeners.
Deleting component screenshots from appmaker
Component screenshots are now loaded from each component's thumbnail tag from appmaker-components.
Add component button was getting overlapped.
Merge pull request #459 from lpachols/discover

Updated discovery popup.