Change tab hide button icon to an eye and add search option

[knolleary]

• New feature (non-breaking change which adds functionality)

This is technically a new feature that addresses a usability concern with the hide-tabs feature. I propose to include this in 2.1.4 rather than wait two months for 2.2.0.

As such, want to get sign-off from @dceejay as this is an exception to our normal way of working.

This PR improves the workflow around hiding tabs a bit. Specifically:

• the icon is changed from the xto by the eye icon. Repeated feedback told us users felt the x implied they were deleting the tab rather than hiding. Changing the icon to the more benign eye is less alarming and more related to visibility rather than deletion.

• moreso, when you hover on the tab the icon is the open eye. When you hover over the eye it closes. This also helps reinforce the purpose of the button.

  

• The tab dropdown menu has a new option at the top if you have hidden flows that tells you how many hidden tabs there are. Clicking on this option opens the search dialog which will list the hidden flows.

  

I think this is a much needed improvement to the hide flows workflow.

[dceejay]

👍 from me. I would classify the icon change as a bug fix so worthy of release. The search option while yes an extra is only a small extra and fixed usability. The first outweighs the second by a wide margin imho.

[coveralls]

Coverage remained the same at 67.363% when pulling a824b69 on tab-buttons into d9f976b on master.