Improve robustness of the input parser.

[xileF1337]

Problem description

The input parser is very sensitive to whitespace (errors). A single, empty line at the end of the input causes it to choke on the input. Some of the columns of the input files cannot be parsed if they are separated by multiple spaces, however, structure and energy of the built-in "small example" are sometimes separated by two spaces. Allowing multiple spaces would allow to format the input in a more human-readable manner.

Additionally, there is no reporting of parser errors to the user. The visualization simply gets stuck at the "Loading..." stage.

Expected behaviour

1. The parser should skip over blank lines.
2. The parser should separate the columns on any consecutive whitespace, be it a single space, multiple spaces, tabs etc.
3. There should be an error message when encountering parsing errors, ideally telling the user which part of the file caused the error and / or how it should actually look like.