Refactor LocalRepositoryModel, RemoteRepositoryModel, RepositoryModel and IGitService

[jcansdale]

This group of classes and interfaces have a number of issues that make them difficult reason about and test.

Some issues

• RepositoryModel, LocalRepositoryModel and RemoteRepositoryModel aren't models at all
• They depend on and hold a reference to IGitService
• LocalRepositoryModel contains mutating methods like Refresh
• LocalRepositoryModel contains utility methods like GenerateUrl

Plan of attack

• Move construction of LocalRepositoryModel into IGitService
• Convert RepositoryModel and LocalRepositoryModel into pure models
• Remove the interfaces (because interfaces aren't needed for POCO types)
• GenerateUrl is only used by LinkCommand so move that there as a private method

Questions

Should the models be mutable or immutable?

@grokys said:

immutable is easier to reason about, but most of our other models are mutable
note that most of our other models are mutable only because the syntax for initializing mutable instances is a lot more readable than for immutable instances

@jcansdale said:

i'd be inclined to keep them mutable for the moment, so we're refactoring less code initially

[jcansdale]

Closed by #2028