specify zoom on tree by clade in URL

[emmahodcroft]

This PR should allow specification of the 'zoom' of the tree by specifying clade= in the URL. Clade is specified by clade_annotation in the tree.json and is what currently draws branch labels onto the tree (if specified).

If the user zooms in on a clade this should change the URL, and if specified in the URL, should load accordingly. Could probably do with a bit more testing, but I think it plays nicely with everything else.

This was a little tricky as applyInViewNodesToTree in actions/tree.js (sets visibility of nodes) modifies node.shell which does not yet exist at the point the URL queries are being 'read.' I've gotten around this by creating node.inView which is then used to set shell when it's created later (in components/tree/phyloTree/phyloTree.js constructor). I don't think this messes anything up, but perhaps there's a neater way.

Should resolve issue 520

Allowing clades to be specified in modular augur by AA should hopefully be possible via the branch clade in augur

[jameshadfield]

This looks great! Code looks good and couldn't find any obvious bugs.