Implement StorageItem plugin system. 

Includes an initial resize plugin that resizes 
and uploads a few reduced size images to the same
storage location as the original image and records
them in metadata.
Change StorageItemPlugin to be an interface instead of an abstract class.
Rename to StorageItemListener and chance process(…) to afterSave(…).
Changes version to 2.1-SNAPSHOT.
Fixes dimension calculation using the calculated dimension of the previous image edit rather than the original image dimensions.
Implements a basic dimension calculation for the DIMS rotate command.
Adds HtmlGrid.divide for later optimizations.
Adds CssUnit.equals.
Improves HtmlWriter.grid markup and styling consistency.
Merge branch 'release/2.0'
Adds reload to $.frame.
Adds HtmlWriter.grid that accept a boolean on whether it should inline CSS.
Improves the error messages on malformed input to HtmlGrid.
Adds HtmlWriter.grid debugging via _grid=true request parameter.
Fixes HtmlWriter.grid producing wrong styles when using non-inline CSS.
Makes it an error to have display: grid without grid-template declaration.
Adds logging to when CSS grid is detected.
Hack for fr units not expanding the content area in HtmlWriter.grid.
Increase the number of padding characters to ensure that the grid fills the width on bigger screens.
Adds webapp source related methods to CodeUtils.