Left panel timeline management

[Annoraaq]

Much of the diff stems from Pulling out a generic TimelineComponent that provides slots to customize the template. It can now be used to display chips (TimelineChip) or table rows (used inside TimelinesTable).
I also added a slot to the UploadForm component to make it more generic and not restrict its usage to buttons. The specific one is now called (UploadFormButton).

[jkppr]

Thanks a lot for this great feature. I fixed some minor UI stuff myself but please take a look at the following comments.

[berggren]

Drive-by comment: We use two different styles for search input in the left panel.

1. Let's stay consistent and choose one. Personally I like the old one with a bit less padding around.
2. Maybe hide the search if number of timelines is less then perhaps <5 ?

[berggren]

1. Do we need the horizontal line? IMO it adds a bit of unnecessary clutter.
2. Maybe reduce the size of the "Timelines" title? It's a bit out of place, font size wise.

[jkppr]

Thanks for the input @berggren . I have included your recommended changes in this PR.

[jkppr]

lgtm
thanks for this great feature!