Refactor band-imagery plugin for extensibility

Change of class names:
* .wdn-scroll-watch is used on all elements which have scrolling effects
* .wdn-scroll-watch.flipbook.lerp for flipbooks
* .wdn-scroll-watch.locked for locked regions
* .wdn-scroll-watch.flipbook.locked.lerp for a locked flipbook

This will allow us to add new transition features like:
* .wdn-scroll-watch.lerp.scale inerpolate the scale of a figure
* .wdn-scroll-watch.lerp.rorate inerpolate the rotation of a figure
etc
Merge branch 'develop' of github.com:unl/wdntemplates into band-imagery

Conflicts:
	wdn/templates_4.0/scripts/band_imagery.js
Add the ability to transform the scale of an element
Add support for altering opacity with scroll
Add opacity change sample
Merge branch 'develop' of github.com:unl/wdntemplates into band-imagery
Remove unused class
Merge branch 'develop' of github.com:unl/wdntemplates into band-imagery
Performance: remove nth-type selectors and use numeric indexes
Remove unused variable
Remove lerp class in favor of data-lerp attribute

The data-lerp attribute will contain a list of lerp-able features, e.g.
data-lerp="opacity scale"

Accordingly, the start and end datab attributes will be specific to each
feature, e.g. data-lerp-opacity-start="#startopacity"
Update documentation references for opacity function
Merge pull request #591 from saltybeagle/band-imagery

Refactoring & new features: Band imagery opacity and scale altering