Rename to SOLPS Tutorials

[hromasova]

• All instances of "the SOLPS wiki" have been renamed to "SOLPS Tutorials" in anticipation of the repository being renamed. Some solps-doc references remain (such as in links to the B2 switch documentation in extras). These are to be fixed in one fell swoop once the ReadtheDocs site is online and links can be properly debugged.
• The documentation has been rewritten to sound more professional. Emotions have been suppressed. We are now in the business of pretending that we know what we're doing.
• Instructions how to contribute to SOLPS Tutorials have been moved from the README to a separate Contribute tutorial.