Addresses issue #138

The main goal of this PR is to add code styling rules and fix any violations.

Added the latest version of StyleCop.Analyzers to each main project, including a stylecop.json file and a default .editorconfig ruleset.

Have kept the default set of SA rules with the exception of the following:

# SA1633: File should have header
## Justification: not required in each indiviaul file as a top level license file exists
dotnet_diagnostic.SA1633.severity = none

# SA1101: Prefix local calls with this
## Justification: this conflicts with the default .editorconfig ruleset
dotnet_diagnostic.SA1101.severity = none

I have also temporarily disabled documentation rules (these will be tackeled under a separate issue) and obsolete code warnings (until the model code can be regenerated to use the case-corrected methods.

Fixed nearly all rule violations accross:

• ModelGenerator
• NHapi.Base
• NHapi.SourceGeneration
• NHapi.NUnit
• NHapi.Base.NUnit
• NHapi.NUnit.SourceGeneration

I have done limited refactoring and spelling correction, but I think that this should be addressed more thoroughly under a separate issue.