Add timeline to navigate through history

Currently

There are 2 ways to highlight the dates:

1. filter by date (in the filter menu)
2. display a capture date rendering (in the layer menu)

We could imagine a new "timeline mode" with a dedicated button next to the filters.

Display a timeline over the map

This button would display a timeline down the screen and activate the capture date layer:

Highlight on hover

When the user hovers a specific month on the timeline, only display them on the map:

Dynamic change of the color

The color range should always be from yellow to dark red.

So it should adapt from the dates of the pictures in the current screen dynamically. This is described in issue #323

Dynamic change of the time range

The time range should also reflect the pictures displayed within the current screen. So it should change from years to months or days depending on the bbox.