Deps map collection spec update, RepoSpec->RepoSpec,ReqSpec split, semver more

[alikins]

Replacing use of 'semver' module with 'semantic_version, and start using semantic_versions.Range() for specifying dep/req version requirement expressions.

Split 'RepositorySpec' into 'RepositorySpec' (data that identifies a particular repo or collection) and a RequirementSpec (data that could match more than one collection)

semver->semantic_version because:

• galaxy uses it (and 'semver')
• the 'Spec' support in semantic_version is more useful than 'semver' limited support
• the 'semantic_version' Version is a little easier to deal with than semver.VersionInfo (mostly the 'partial' support)