Improve inputs

[Joaquimmnetto]

Description

Several small refactors and improvements to input-related classes.

• Renames VersionCodeScheme to VersionCodeSchemes to keep consistency with the VersionSchemes name.
• Gives preference to Property<T> instead of Provider<T> for input extension types
• Adds prefix to VersionPluginConventions and reformat the class to be more similar to whats in the newer plugins.
• Moves out extension convention setup from DefaultVersionPluginExtension constructor.

Based on #59 , please merge that first.

Changes

• All extension properties now are Property<T> instead of Provider<T>
• prefix property now can be set through environment or gradle properties.

[Larusso]

Ok I see that you addressed some comments I made in the Original PR #58 Would it be possible to combine these PRs? If not lets see how we best merge the changes