adding mouse down event
fixes
Merge branch 'master' of https://github.com/biasmv/pv into create-mouse-down-events
atom picked event
add rotate and single variable (zoom) animation.
add camera zoom, rotate, translate in one operation.
allow chains for fitTo
Merge branch 'chain-centre'
Merge branch 'create-mouse-down-events'

# Please enter a commit message to explain why this merge is necessary,
# especially if it merges an updated upstream into a topic branch.
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Merge branch 'fix-original-background'

Conflicts:
	src/viewer.js
fix for selection events.
Merge branch 'create-mouse-down-events'
Merge branch 'master' of https://github.com/biasmv/pv

Conflicts:
	src/viewer.js
remove animation by default
Merge branch 'master' of https://github.com/biasmv/pv into create-mouse-down-events
adding doc and refactoring event framework
a few tweaks to event listener documentation
Merge commit 'pull/origin/40'
add back the center on atom doubleClick behavior

This restores the 'centering' behaviour, but makes it possible
to opt out of it by passing a null atomDoubleClick when constructing
the viewer. addListener now also understands the special callback
value 'center' to install the center on atom event listener, which is
granted a little tricky to write because of all the transformation
code.
document animateTime