Don't rename 'unnamed' tabs upon deletion of other tabs

[AdaShoelace]

This PR aims to solve issue #474.
I decided to put the logic in Tab::new. This approach felt the "cleanest" to me.
If this breaks any style guides or should be done differently for other reasons please let me know and I'll change it.

[a-kenji]

Thank you, this is already pretty great and
I think including it in tab does make a lot of sense!

There is still one thing that I would like to see a little bit different:

When opening a tab and not really caring about the name,
I think I know what you want to convey with the (unnamed), but I think it
does take up too much space. And should be fine with being omitted.

[AdaShoelace]

Thank you, this is already pretty great and
I think including it in tab does make a lot of sense!

There is still one thing that I would like to see a little bit different:

When opening a tab and not really caring about the name,
I think I know what you want to convey with the (unnamed), but I think it
does take up too much space. And should be fine with being omitted.

"(unnamed)" has been removed.

[a-kenji]

Awesome, thank you!

[ammkrn]

@a-kenji

It seems like some underlying map of tabs to numbers still exhibits the old behavior. If I have tab1, tab2, tab3, tab4 and closetab2, the remaining tabs are tab1, tab3, tab4, but in tab mode, pressing the 2 key jumps to tab3 and the 3 key jumps to tab4.

If other people are observing this I can take a look at it. Hints for where to look would be appreciated. (I'm using 0.13.0 on macOS).

[a-kenji]

@ammkrn,
Thank you for the input!
This is correct, but sadly still confusing behaviour.
The tabs are now named that way by default, but the keys
map to the position in the tab. I hope with #557 we can show
the number of the tab and then the name of the tab with a
running program/shell behind.

I believe we want (am happy about more input):
To go to a specific tab-name: #379. (An ongoing pr atm).
To go to a specific tab#. (The current 2 behaviour).

I imagined this here to be in scope of #557:
To show the number of the current tab.
To show the name of the current tab. (possibly with name of currently running process)

I am not sure if showing the number of the current tab would already
be desirable if the tab name wasn't already updated by the current
running program.

[ammkrn]

Thanks for clearing that up; I look forward to seeing how those solutions work out.