This splits apart the download modal react component into two: one for the main modal layout, and another for the download buttons. This improves separation and paves the way for improvements to the download buttons. There should be no changes in behavior arising from this commit.

Previously this triggered an automatic screenshot (SVG) download, which was dev-only, undocumented functionality that made it into production.

Here we map "d" to open the download modal which is both more expected, and helpful for the current work. This key shortcut can either be removed in this PR or documented and released as-is.

Previously certain downloaded files (e.g. trees) represented all data, certain files only represented selected (visible) data (e.g. entropy) and some could do both (e.g. there were two metadata buttons).

This commit moves to having all buttons behave in a consistent manner -- if the data is subsetted (filtered, zoomed etc) then only the visible nodes will be part of the download.

All file exports _except_ trees are updated in this commit.

(See previous commit message for context).

Exported trees now represent the visible (and in-view) tree.

Note that exported trees of filtered datasets often contain nodes higher (more ancestral) than the expected root. This is the bug reported in #1240.

Similar to current Newick export except in a format conforming with BEAST such that it can be read by FigTree.

This makes behavior consistent with the idea that downloaded data represents the current view. It also prevents a bug when trying to download a temporally scaled tree for a non-temporal dataset.