Update requirements.

install.sh now uses requirements.txt to determine which pip packages
to install.
Dynamically read variables from OpenDAP Server.

Works with 3D files
Added message when there are no datafiles

Shows a helpful message rather than an empty table.
Merge pull request #4 from Andrew-Dunn/no_datafiles

Added message when there are no datafiles
Retrieve variables from datafiles.

Retrieves selected variables from the datafiles.
Will retrieve the identifier, name and number of dimensions.
Only valid variables will be presented as options.
Also updated the latest dump to have an unlimited size for the json
info and emptied the computation and datafile tables.

Don't forget to run `pip install Pydap` if not using **install.sh**
Merge pull request #5 from Andrew-Dunn/getvariables

Retrieves variable info from the netcdf datafiles.