elapsedTimeControlView: minimize updates onchange
less: remove custom overflows

overflow-hidden and overflow-scroll were both creating a 1px line
padding on the left of the videolinkshell controls toolbar that hid any
overflow underneath it
videoLinkShell: add remix view play/pause controls

also add elapsed time view
mouseTrackingView: reject false option (no `?`)

the offsetFromElement option to _percentMouseDisplacement should be
rejected if falsy
util: adjust bound utility: always return a number

override this requirement by passing enforceNumber: false
slidingBarView: warn on invalid internalViews
test: bugfix requiring wrong file
config: remove old reference to jQuery UI
less: remove styling for old jQueryUI rangeslider
rangeSliderView: add class to subview range bar
slidingBarView: accept internalView not in array
mouseTrackingView: require $el parameter in method

_mouseOffsetFromElement now throws an explicit error when called without
a value
valueSliderView: create ValueSliderView
sliderBars: add TODO note to abstract into parent

Quite a lot of functionality is shared between Value and Range
Slider Views; it should be factored up into a parent class to dry up the
code
slidingBarView: bugfix: only get own internalViews

previously would grab internalViews of children and append content
multiple times
progressRangeSliderView: create PRSV
test: add tests for elementInDom utility
util: add toPercent and fromPercent utilities
util: add comment to util.bound utility
timeRangeInputView: use util.bound utility