support to add local shape files (topojson, geojson)

Addresses: #10

Changelog

Added support for uploading vector shape files (.topojson & .geojson)
The shape file is added as a new layer on top of the existing layers. Any newly added layer will remove existing layer added before.
The app uses Redux for keeping track of shape type & data. The data is added locally on the client without hitting the server. (Redux portion has been rewritten.)
The shape data contained in files can be large which may not fit in URL strings, and may encounter issues while encoding & decoding. Hence, it is done via Redux.