Ability to control alignment in fitSelection() and "zoom in" tool + typescript support

[tblaette]

Added ability to control alignment in fitSelection() and "zoom in" tool:

• enabled to specify SVGAlignX and SVGAlignY parameters in fitSelection():
  • fitSelection(value, selectionSVGPointX, selectionSVGPointY, selectionWidth, selectionHeight, SVGAlignX=ALIGN_LEFT, SVGAlignY=ALIGN_TOP)
  • refactored fitToViewer() to call the new fitSelection() function internally
• made the zoom in tool to respect the toolbarProps.SVGAlignX/Y props. If for instance toolbarProps.SVGAlignX is set to center, drawing a rectangle to zoom in will now center the selected area in the view.
• updated the documentation to reflect the changes above

Added typescript support:

• added index.d.ts file and updated package.json accordingly
• the index.d.ts file is based on the types defined in the DefinitelyTyped repo:
  • https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/react-svg-pan-zoom/index.d.ts
• the types have been updated to reflect the latest API of react-svg-pan-zoom and include the added alignment parameters to fitSelection() as well.

Note: if you prefer to not have typescript support in your project, see PR #225