Improve the structure class

The previous structure class exposed too much of it as public
attributes. Not it has been improved by adding several methods for its
manipulation.
Add the editorconfig file

To avoid the problem with the tab and facilitate the possible usage of
multiple editors for the project, the .editorconfig file is added for
the project with some basic python settings.
Add the gjf reader

A gjf reader is tentatively added to parse the Gaussian input format.
Also a function for terminating the program due to unrecoverable errors
is added in the utility module.
Add the bond resolution module

A module is added that is able to resolve multiple as well as partial
bonds into list of cylinders. Also many other information is attached to
the data structure as well to facilitate possible future further
processing.