Added base methods to ResourceViewer.

These methods must be overridden by implementing classes:
load()
resize()
Buttons in the ResourceViewer top panel are now conjoined
Top panel takes up minimal space, and is translucent before mouseover
Adapted ErrorScreen from resource-audio branch
ResourceViewers can now display an error message

Simply use showError([message]) and hideError().
Adapted ProgressBar from resource-audio branch
ResourceViewers can now display and hide animated progress bars

Use the following methods to manipulate the progress bar:

- showProgressBar([initialLoadingMessage])
- updateProgressBar(percent, [loadingMessage])
- hideProgressBar()

If initialLoadingMessage is not provided, a default message will be displayed instead.
Tweaked progress bar to display faster transitions on percentage updates
Merge pull request #37 from blackhydrogen/boilerplate

ResourceViewers enhanced with more visual updates and functionalities
VideoResourceViewer now shows and hides a progress bar when necessary
Abstracted panning & zooming functionality.
Fixed custom filters bug.
Moved panZoomWidget.js to static.
Merge pull request #38 from blackhydrogen/resource-image

Resource image
Merge branch 'master' into resource-video
VideoResourceViewer now uses the PanZoomWidget
MediaControls can now display a single buffer indicator
VideoResourceViewer now reports buffer progress to the MediaControls
MediaControls can now display multiple buffer indicators
VideoResourceViewer now displays multiple buffers where possible