Issue 356 Add live updates to dashboard widget

[johnregan3]

Live Updates for Dashboard Widget.

• "Enable live updates" checkbox
• Default setting to true on install
• Configure heartbeat response
• One method to fire on heartbeat_recieved to handle Dashboard and Stream Page requests (DRY)
• One method to generate list items for dashboard widget, whether initial page load or heartbeat
• JS to handle updating the Dashboard
• When new items are added, remove correct number to keep records_per_page
• Only display updates on first page of results
• Highlighting/Fadeout of new items

Fixes #356

@fjarrett

[frankiejarrett]

@johnregan3

1. When I checkout the branch the option is not checked by default. Since no DB value exists to explicitly turn it off, it should be checked and turned on by default.
2. I think we should be using similar logic to what was used in the list table with the live update values being on and off strings.

[johnregan3]

@fjarrett The option is now enabled by default, using similar logic to the Stream Live Update checkbox. Tested by using delete_option on page load, and "Enabled" is the default state.

[frankiejarrett]

@johnregan3 Nice work! Now please merge master into this branch and resolve any conflicts. And lastly, please remember to issue against the develop branch next time.

[johnregan3]

@fjarrett Sorry, man. I get mixed up between projects. I'll get it fixed.