Refactoring volume checking to display wells in colours.

Refactored plate, gel & rack labware views to behave similarly.
Refactored volume check model to pass appropriate labware view.
Added thresholds to pipeline_config.json.
Added CSS classes for thresholds.
Removed fills from tubes in rack.svg.
Corrected barcode text element in rack.svg.
Fixed volume checking so that it works correctly.
Refactor drop zone handling into common area.

Added the drop_zone view that deals with drag-n-drop file handling.
Refactored all controllers using drag-n-drop to use this view.
Refactored the rack scan view to use the drop_zone view.
Fixed a CSS issue that was preventing drop zone highlighting.
Reworked all drop zone HTML to be uniform across the project.
Refactoring display of tubes & racks

Added standard mappings from labware to labware view data.
Set up the various controllers that need the above.
Fixed up a load of issues with the rack scan model.
Removed unused SVG files.
Made tube behave more like rack and plate.
Refactored standard presentation to use aliquot type.
Changed waste tube concept to work on tracked

Removed all of the waste tube code & views.
Copy "tracked" information into resource when created.
When presenting tube display the "unused" element.
Hide all detail text in SVG.
Added legends to the labware

Added the legends to the labware and hid them by default.
Display the correct legend based on state of the rack scan process.
Adjusted the colours for DNA/RNA to be more distinct.
Fixed a bug in the naming of CSS classes.
Merge pull request #305 from mattdenner/refactor_rack_display

Refactor labware display & volume checking information