Implement Hubs Dashboard

[sengineer0]

This PR implements a new Dashboard, which will show all existing Hub connections, with some basic information

• The dashboard should show all hubs (one hub as one box/tile) in a grid view
• Each hub tile should display some basic information (name, logo, some stats likes # of data srcs, builds etc, # of active tasks)
• Click a tile should connect to that hub
• Should have an interface to customize the hubs to be included in the dashboard, or other preferences. These preferences can be saved on browser-side
• Some hubs may not be accessible at a particular moment, which is fine and should not impact the display of other working hub tile.
• Should allow to switch between the dashboard view or the current connection view as the default landing page. The preference can be saved on browser-side as well.

Ref: biothings#110

[newgene]

@sengineer0 I tested this WIP version, it looks very nice! See the screenshot I have:

Just a few polishing notes:

• click each box should connect to that hub instead of going to the connection interface and then click the ok button
• "# of documents" should show comma separated, or you might set all numbers should be displayed this way
• add a "refresh" button
• add loading icon while loading hub status, and display an error icon when a hub is not accessible
• change the hover-over cursor to indicate it's clickable if you allow clicking anywhere in the box to the hub.
• try to make the size of boxes equal, so they align well. Sometime if a title is too long, ok to make it overflow instead of folding into two lines then breaking the alignment. In this case, we will know we should fix the title to make it shorter.
• If it's easy to add, making this direct URL work too: http://localhost:8080/#/dashboard, (regardless the saved preference)
• The button "switch to simple mode" probably should just be called "Create new connection" with an icon consistent to the one in the connection dropdown menu.
• Add the consistent icon for "Hubs Dashboard" in the dashboard view.

[sengineer0]

• click each box should connect to that hub instead of going to the connection interface and then click the ok button (It's already implemented. the connection interface only be shown when the hub is not accessible)
• "# of documents" should show comma separated, or you might set all numbers should be displayed this way
• add a "refresh" button
• add loading icon while loading hub status, and display an error icon when a hub is not accessible
• change the hover-over cursor to indicate it's clickable if you allow clicking anywhere in the box to the hub.
• try to make the size of boxes equal, so they align well. Sometime if a title is too long, ok to make it overflow instead of folding into two lines then breaking the alignment. In this case, we will know we should fix the title to make it shorter.
• If it's easy to add, making this direct URL work too: http://localhost:8080/#/dashboard, (regardless the saved preference)
• The button "switch to simple mode" probably should just be called "Create new connection" with an icon consistent to the one in the connection dropdown menu.
• Add the consistent icon for "Hubs Dashboard" in the dashboard view.